A simple method for measuring a picogram of acetylcholine using the clam (Mya arenaria) heart.

1. A simple and reliable method is described for assaying 1 pg or less of acetylcholine (ACh) using a strip of clam (Mya arenaria) heart.2. Clam heart preparations generally are extremely selective for ACh. The preparation described is at least 10(5) times less sensitive to the following: acetyl coenzyme A, adrenaline, choline, dopamine, gamma-aminobutyric acid, glutamic acid, histamine, 5-hydroxytryptamine and noradrenaline.3. Because this preparation is one of the most sensitive known for detecting ACh, it should prove useful for assaying particularly low levels of this substance in biological extracts.