Three adult rhesus monkeys were trained to stable performance baselines on a delayed match-to-sample (DMS) procedure. Subject-initiated trials resulted in brief presentations of a sample color stimulus (red, green, or blue) with matching performance tested after retention intervals of 0, 4, 8, and 16 seconds. The effects of graded doses of atropine SO4, benactyzine HCl and physostigmine salicylate on performance were studied. Only atropine produced a clear interaction between drug and retention interval with the greatest impairments being observed at the longest delays. Benactyzine only affected overall error rates, while physostigmine did not disrupt matching accuracy. The two highest doses of each compound produced reliable elevations in session times and drug-specific changes in the pattern of performance. The results with atropine confirm and extend previously reported work with scopolamine indicating a critical role for cholinergic mechanisms in short-term memory.