diff --git a/README.md b/README.md
index 2f966ea4b08ab195e62aa08e4f6ff73353d12307..3660d7b2a0c87c3e393d75b3d6a427bf092e8b7c 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,7 @@ Each patch has a disease state.
 ;- State variables
 patches-own [
   state
+  infected-neighbours
 ]
 ```
 
@@ -41,10 +42,12 @@ set R 3
 ```netlogo
 ;- Go
 to go
+  infect-patches
   update-patches
   tick
 end
 
+; ==> Infection.
 ; ==> Update patches.
 ```
 
@@ -57,6 +60,14 @@ end
 to setup
   clear-all
   ; ==> Setup disease states.
+
+  ask patches [
+    set state S
+  ]
+  ask one-of patches [
+    set state I
+  ]
+
   update-patches
   reset-ticks
 end
@@ -66,6 +77,37 @@ end
 
 ### Submodels
 
+#### Infection
+
+```netlogo
+;- Infection
+to infect-patches
+  ask patches [
+    set infected-neighbours 0
+  ]
+  ask patches with [ state = I ] [
+    ask neighbors [
+      set infected-neighbours infected-neighbours + 1
+    ]
+  ]
+  ask patches with [ state = S ] [
+    if random-float 1 < calc-infection-prob [
+      set state I
+    ]
+  ]
+end
+
+; ==> Infection probability.
+```
+
+```netlogo
+;- Infection probability
+to-report calc-infection-prob
+  report 1 - (1 - beta) ^ infected-neighbours
+end
+```
+
+
 #### Visualization
 
 ```netlogo
diff --git a/nlogo/Model.nlogo b/nlogo/Model.nlogo
index 9437b79e9e9fae528c8e37d7be911ce7aab46025..d55b648e82596c4f3b009beb623119387420c299 100644
--- a/nlogo/Model.nlogo
+++ b/nlogo/Model.nlogo
@@ -1,9 +1,9 @@
 __includes["Code.nls"]
 @#$#@#$#@
 GRAPHICS-WINDOW
-220
+230
 10
-733
+743
 524
 -1
 -1
@@ -30,7 +30,7 @@ ticks
 BUTTON
 10
 10
-80
+110
 50
 NIL
 setup
@@ -45,9 +45,9 @@ NIL
 1
 
 BUTTON
-90
+115
 10
-160
+215
 50
 NIL
 go
@@ -59,7 +59,22 @@ NIL
 NIL
 NIL
 NIL
+0
+
+SLIDER
+10
+62
+215
+95
+beta
+beta
+0
 1
+0.2
+0.01
+1
+NIL
+HORIZONTAL
 
 @#$#@#$#@
 ## WHAT IS IT?
@@ -90,5 +105,5 @@ true
 Line -7500403 true 150 150 90 180
 Line -7500403 true 150 150 210 180
 @#$#@#$#@
-0
+1
 @#$#@#$#@