A simple new method, the "tape test" has been developed for studying the enhancement of learning by drugs in "learning-dull" rats. A piece of adhesive tape is pressed on the left front pad of the rats. The time of tape removal by the animal, i.e., the problem-solving time is measured. In our experiments the selected learning-dull rats were used which were unable to remove the tape within 60 s observed on 3 consecutive days. The problem-solving ability of the rats was studied on 4 consecutive days, by posttrial administration. The problem-solving ability was found to be increased after treatment with different drugs such as para-chlorphenylalanine (PCPA), pemolin, orotic acid, vitamin B12. The stimulatory effect of vitamin B12 could be inhibited by vincristine.