We report the effects of aqueous extracts of the microalgae Dunaliella tertiolecta Butcher (Chlorophyceae) and Phaeodactylum tricornutum Bohlin (Bacillariophyceae) on oxotremorin-induced cholinergic symptoms, amphetamine-induced hypermotility, pentylenetetrazole-induced convulsions, and Rota-rod test performance. Both extracts significantly reduced rectal temperature, spontaneous motor activity, and time on the Rota-rod and increased the number of mice falling off the rod before 180 s, but neither protected against pentylenetetrazole-induced convulsions or against oxotremorin-induced tremor, salivation, and diarrhoea.