diff --git a/Cargo.toml b/Cargo.toml
index 40d5063..d2ae33c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,4 +5,5 @@ edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
-[dependencies]
\ No newline at end of file
+[dependencies]
+bitvec = "1.0"
\ No newline at end of file
diff --git a/src/misc/dense_store.rs b/src/misc/dense_store.rs
index 8afbce2..32123ef 100644
--- a/src/misc/dense_store.rs
+++ b/src/misc/dense_store.rs
@@ -13,6 +13,10 @@ impl<T> DenseStore<T> {
         Self { items: Vec::new() }
     }
 
+    pub fn len(&self) -> usize {
+        self.items.len()
+    }
+
     pub fn get(&self, index: Index<T>) -> Option<&T> {
         self.items.get(index.into_raw())
     }
diff --git a/src/sandbox/mod.rs b/src/sandbox/mod.rs
index ddfc797..d11c392 100644
--- a/src/sandbox/mod.rs
+++ b/src/sandbox/mod.rs
@@ -2,6 +2,8 @@
 
 mod serialize;
 
+use bitvec::vec::BitVec;
+
 use crate::{
     latest::ModInfo,
     misc::{
@@ -20,6 +22,7 @@ pub struct Sandbox {
     components: ObjectStore<ComponentInfo>,
     wires: ObjectStore<WireInfo>,
     nets: DenseStore<NetInfo>,
+    net_states: BitVec<u8>,
 
     next_type: u16,
     component_types: HashMap<String, u16>,
@@ -40,6 +43,7 @@ impl Sandbox {
             components: ObjectStore::new(),
             wires: ObjectStore::new(),
             nets: DenseStore::new(),
+            net_states: BitVec::new(),
 
             next_type: component_types.values().copied().max().unwrap_or(0),
             component_types,
@@ -270,6 +274,9 @@ impl Sandbox {
     }
 
     fn make_net(&mut self) -> NetId {
+        assert_eq!(self.nets.len(), self.net_states.len());
+
+        self.net_states.push(false);
         NetId(self.nets.insert(NetInfo {
             wires: HashSet::new(),
             pegs: HashSet::new(),
@@ -287,6 +294,11 @@ impl Sandbox {
             for peg_id in &renamed.pegs.clone() {
                 self.get_peg_mut(peg_id).unwrap().net_id = NetId(rename.dest);
             }
+
+            // Perform the same swap-remove in net_states:
+            self.net_states.swap_remove(rename.dest.into_raw());
+
+            assert_eq!(self.nets.len(), self.net_states.len());
             Some(net)
         } else {
             None
diff --git a/src/sandbox/serialize.rs b/src/sandbox/serialize.rs
index d879fe3..6be59bc 100644
--- a/src/sandbox/serialize.rs
+++ b/src/sandbox/serialize.rs
@@ -1,5 +1,7 @@
 //! Conversions between the Sandbox editor and Blotter serialization types.
 
+use bitvec::vec::BitVec;
+
 use crate::latest as blotter;
 use std::collections::{HashMap, HashSet};
 
@@ -101,6 +103,9 @@ impl From<&super::Sandbox> for blotter::BlotterFile {
             components.push(ser.serialize_component(component_id, component))
         }
 
+        let mut states = sandbox.net_states.clone();
+        states.set_uninitialized(false);
+
         Self {
             game_version: GAME_VERSION,
             save_type: blotter::SaveType::World,
@@ -120,7 +125,7 @@ impl From<&super::Sandbox> for blotter::BlotterFile {
                 .map(|(_id, wire)| ser.serialize_wire(wire))
                 .collect(),
             circuit_states: blotter::CircuitStates::WorldFormat {
-                circuit_states: vec![], //TODO
+                circuit_states: states.into_vec(),
             },
         }
     }
@@ -218,6 +223,19 @@ impl From<&blotter::BlotterFile> for super::Sandbox {
             file.mods.clone(),
         );
 
+        match &file.circuit_states {
+            blotter::CircuitStates::WorldFormat { circuit_states } => {
+                sandbox.net_states = BitVec::from_slice(circuit_states);
+                for _ in 0..8 * circuit_states.len() {
+                    sandbox.nets.insert(super::NetInfo {
+                        wires: HashSet::new(),
+                        pegs: HashSet::new(),
+                    });
+                }
+            }
+            _ => panic!("unsupported circuit state format"),
+        }
+
         for component in &file.components {
             let id = sandbox.insert_component(de.deserialize_component(component));
             de.register_component(component.address, id);
@@ -230,8 +248,6 @@ impl From<&blotter::BlotterFile> for super::Sandbox {
                 .unwrap();
         }
 
-        //TODO load circuit states
-
         sandbox
     }
 }