Seven oral antidiabetics (chlorpropamide, glibenclamide, glipizide, gliquidone, glymidine, tolazamide, and tolbutamide), and 14 diuretics (bemetizide, bendroflumethiazide, benzylhydrochlorothiazide, bumetanide, butizide, chlortalidone, furosemide, hydrochlorothiazide, hydroflumethiazide, indapamide, piretanide, polythiazide, trichlormethiazide, and xipamide) were investigated for potential phototoxicity in vitro using a cell culture model and in vivo in hairless mice. After exposure to broad band UVA, the majority of the substances tested in vitro yielded phototoxic action leading to loss of culture forming ability. In vivo, all tested substances induced edema or ulceration, and lead to a significant increase in skin fold thickness of the mouse skin. In all a number of substances not described to induce clinical photosensitivity nor phototoxicity in vitro or in vivo were detected in our testing. In determining potential photosensitizers, it seems important to utilize different test methods, as not all substances will exhibit action in a given assay.