This paper reports several studies of the effects of pentylenetetrazol on learning in mice. The first three studies indicated that, for several strains and learning tasks, the degree of facilitation produced by posttrial injections of subconvulsive doses of pentylenetetrazol varied with the different strains and experimental conditions used. The fourth experiment showed that facilitation of learning is obtained only when the drug is injected within 15 minutes before or after training. Other findings indicated that the convulsive and lethal doses of pentylenetetrazol depend upon the animals' deprivation state and that when given to rats in subconvulsive doses, the drug produces EEG effects which are seen within minutes after injection and which last for less than one hour. We interpret the results of these learning experiments as indicating that pentylenetetrazol enhances learning by affecting processes involved in memory storage.