Summary: Previous studies have not demonstrated a consistent relationship between precursors to acetylcholine (ACh) and memory function in normal human subjects. This experiment (N = 80, college students) employed a double-blind mixed design to test the effect of phosphatidylcholine (PCh) on explicit memory. Dose of placebo and PCh was compared at two levels (10 and 25 g) as was time of testing postingestion (60 and 90 min). With 25 g of PCh, which supplies 3.75 g of choline, significant improvement in explicit memory, as measured by a serial learning task, was observed at 90 min postingestion and slight improvement was observed at 60 min postingestion. Further analyses indicated that this improvement may have been due to the responses of slow learners. This is the first study to test the relationship between a single dose of PCh and explicit memory on normal human subjects.