A group of four acidic imidazo[1,2-c]pyrimidine derivatives were subjected to a series of tests in vivo in order to assess their pharmacological activity. Antiinflammatory activity was studied by means of the carrageenin-induced paw edema and pleurisy in rats. Hot plate test and writhing induced by acetic acid in mice were employed to evaluate analgesic activity, whereas the yeast-induced hyperthermia in rats was used to study antipyretic activity. The irritative and ulcerogenic action on the rat gastric mucosa was examined at higher doses. The inhibitory activity on the platelet malondialdehyde production was studied in order to obtain information about the mechanism of action of test compounds.