The drug solvents diethyleneglycol monoethylether (Transcutol), N,N-diethylacetamide, and dimethylsulfoxide were examined for their pharmacodynamic properties in the following tests: i.p. toxicity, "sign pattern", inclined screen test, balance rod test, and potentiation of hexobarbitone sleeping time in mice, spasmolytic activity in the guinea pig isolated ileum, and cardiovascular studies in anaesthetized rats, cats and dogs including the i.v. toxicity. Except for the cat, N,N-diethylacetamide exhibited the highest toxicity; this solvent, too, was particularly potent in inducing behavioural changes and in potentiating hexobarbitone sleeping time. In the isolated ileum the solvents showed unspecific spasmolytic activities with histamine, carbachol, or BaCl2 as spasmogens. After i.v. administration in rats, cats, and dogs the solvents caused cardiovascular effects even in very low doses. Based on the pharmacodynamic properties doses are recommended for each solvent which should not be exceeded without control experiments in the laboratory routine. These tolerable doses do not only depend on the species but also on the test concerned.