The memory effects of citicholine (CCh) and piracetam (Pc) were tested in experiments on mice using the training method with passive avoidance and negative reinforcement (step-through). In single doses of 25, 50, 100 and 500 mg/kg, CCh applied one hour prior to training enhanced to the same degree and statistically significantly the retention of the memory traces in tests both 24 h and 7 days after the training session; Pc in a dose of 500 mg/kg improved the retention in memory tests 24 h after training, but had no significant effect during the tests 7 days after the training. Combined application of CCh and Pc in doses which are ineffective with respect to the memory process (CCh--10 mg/kg and Pc--200 mg/kg) caused a significant enhancement of the retention during the tests both 24 h and 7 days after the training. Scopolamine (2 mg/kg i.p.), applied 30 min prior to the training, manifested a marked amnestic effect during the tests 24 h after the training, but this effect was totally prevented if either CCh in a dose of 50 mg/kg or Pc in a dose of 500 mg/kg were applied before scopolamine. Citicholine in a dose of 100 mg/kg, as well as the combination of 50 mg/kg CCh and 500 mg/kg PC, not only completely prevented the scopolamine-induced amnesia, but they also significantly increased the retention of the memory traces in the scopolamine-treated mice compared with the retention observed in the control animals.(ABSTRACT TRUNCATED AT 250 WORDS)