Comparative tests were made with four mutagens, treating male germ cells, particularly mature sperm, of Drosophila melanogaster. Dominant lethals, sex-linked recessive lethals, sex-chromosome loss and partial loss, and in one test translocations were used as genetic and points. The four mutagens, methanesulphonate (MMS), 2,3,5,6-tetraethyleneimino-I,4-benzoquinone (TEB), I(2,4,6-trichlorophenyl)-3,3-dimethyltriazene (2,4,6-triC1-PDMT), and diethyl nitrosamine (DEN) are known to differ in their chemical properties and mode of mutagenic action. An apparent relationship between dominant lethal induction and other genetic damage was found only with TEB. All four mutagens are efficient inducers of sex-linked recessive lethals. At low concentrations there was no direct concentration-frequency relationships. The two direct mutagens, MMS and TEB were effective in the chromosome loss tests. DEN does not induce translocations or any of the other types of damage studied which can be attributed to chromosome breakage. It is concluded that the sex-linked recessive lethal test is a simple and efficient way of preliminary screening chemical mutagens with Drosophila melanogaster.