Experiments were made on 2- and 18-month-old male rats to test the effects on the acquisition and retention of piracetam, meclofenoxate and four newly-synthesized substances with assumed nootropic action: pyrrolidine derivatives with code names p-F, p-P and A-T, as well as the derivative of para-chlorophenoxypropionic acid, with code name 4-Cl-alpha PA. The method of two-way active avoidance was used, with punishment reinforcement during 5-day training and retention tests on the 14th day after the beginning of training. The agents studied were applied orally in doses of 30 and 150 mg/kg for 3 days (2 days before training and on the first day of training) and then again one hour before the retention testing. The older rats manifested a poorer learning capacity than the younger ones. Piracetam produced the best effect both on learning and on retention. Compounds with code names p-F, p-P and A-T induced an increase in the number of avoidances compared with the controls on isolated days only, according to the tests for acquisition. The favourable effects observed are not in close dependence either on the dose applied, or on the age of the experimental animal. No significant effects were observed under the effect of meclofenoxate and of its structural analogue 4-Cl-alpha PA.(ABSTRACT TRUNCATED AT 250 WORDS)