Four workers employed in the manufacture of ultraviolet-cured inks complained of photosensitivity characterized by an intense burning sensation during sun exposure. Three of these workers developed dermatitis on exposed areas following sun exposure. Six compounds used as photoinitiators in the ink formulations were found to absorb solar ultraviolet radiation. Two preparations of mixed isomers (ortho and para) of amyl dimethylaminobenzoate were found to be phototoxic to Ehrlich ascites cells in vitro and to produce diphasic phototoxic reactions in vivo after topical application on symptomatic workers, asymptomatic workers, or previously unexposed subjects. These responses could be prevented in two subjects by the application of a 10% sulizobenzone sunscreen prior to sun exposure. Two other photoinitiators, Michler's ketone and thioxanthone were phototoxic in vitro but not after topical application in vivo.