Up until now very few investigations have been made to test the possible genetic effects of cadmium. Since ionic cadmium reacts with sulfhydryl groups, its cytogenetic mode of action most probably is connected with - either directly or indirectly - the formation and functioning of the mitotic apparatus. Evidence of this type of mutagenicity has been obtained in plant material. However, results with Drosophila have not as yet revealed a significant increase of mutation frequency after treatment with cadmium. In the present investigation the authors have been testing the possible effect of cadmium on the primary gene action observable in the specific sequence of salivary chromosome puffs of Drosophila. The results are compared with earlier data of the effects of organic mercurials on the prepupal puffs of D. melanogaster. 8 references, 3 figures, 1 table.