R 58 735, a benzthiazole derivative, is a potent antihypoxic agent with anticonvulsant properties. As an antihypoxic drug, it was more potent than any other reference substance in hypobaric hypoxia in mice and in histotoxic dysoxia and nitrogen hypoxia in rats. In the nitrogen hypoxia test, R 58 735 was equipotent in males and females, and the p.o.\i.v. ratio varied from 2.8 to 2.6. The antihypoxic activity of orally administered R 58 735 latested more than 8, but less than 24 hr. The anticonvulsant profile of R 58 735 resembled that of flunarizine, i.e., blockade of the tonic convulsions induced by pentylenetetrazol, allylglycine, or bicuculline, but not of clonic convulsions, except those seen in audiogenic seizureprone mice. In the allylglycine or bicuculline tests, it was more potent than any other reference anticonvulsant. In the bicuculline test, there were no sex-related differences in activity, and the p.o.\s.c. activity ratio was 2.01 in males and 1.74 in females. Following oral administration, the duration of anticonvulsant activity in the bicuculline test was more than 8, but less than 24 hr. In guinea pigs, R 58 735 completely antagonized hypoxia-induced amnesia at a dose of 2.5 mg\kg s.c. Furthermore, it enhanced acquisition of a two-way avoidance task over a broad dose range (0.63–20 mg\kg) in rats.