Solvents were tested for their influence on motivational state, as well as for their sedative effects, after intraperitoneal administration. The following tests were used: open field (exploratory activity, locomotion), activity wheel (running activity), tube test and tilted plane (muscle weakness, incoordination). The agents proved to be similar in causing muscle weakness and ataxia already at low dose levels. Benzene was the most potent in this respect. The three solvents, however, contrasted strongly in influencing motor activity. While benzene and especially toluene exerted CNS stimulation, no such effect could be detected following m-xylene treatment. On the basis of human experiences with these substances it may be suggested that the screening procedure applied in rats might be useful for predicting acute adverse effects in man.