Learning of rats given either piracetam, 2-thio-1-pyrrolidine-acetamide (thioacet) or 2-thio-1-pyrrolidine-thio-acetamide (thiothio) was studied in order to investigate nootropic effects of the compounds. Learning ability was measured using a Y-maze with water reward for the correct choice in a black-white discrimination task. Thioacet and thiothio enhanced learning ability of the rats at doses that were 2.5-10 times lower than those required for obtaining nootropic effects of piracetam. Thus the thio-derivatives of piracetam might be of value for studying mechanisms of action of nootropic drugs.