In the first experiment rats were trained in black-white discrimination, then injected with 7.5, 10.0, or 15.0 mg/kg of pentylenetetrazol (Metrazol) or saline. Injections were given immediately or 15 min following training. The animals were retested 24 hours later. Improved performance was observed for drug groups, but the extent of improvement was a joint function of the amount of drug and the time at which it was given. Animals given 10 mg/kg showed greater retention when injection was delayed. In a second experiment animals were given spaced trials in a position discrimination task, extending over a period of several days. Following each day's, session, animals were injected with pentylenetetrazol or saline at intervals of 0, 5 or 10 min. A maximum facilitation effect was obtained at the 10-min interval.