The data reported in this paper extend earlier results on the effects of hycanthone in Drosophila. The main findings are the following. (1) A refined brood-pattern analysis of hycanthone-induced sex-linked recessive lethals confirmed the specific sensitivity of mid- and late spermatids. Injection of young males 0--20 h old) did not cause a shift in the brood pattern, but tended to produce higher rates of recessive lethals than injection of 4-day-old males, although the difference was not significant. (2) An autosomal recessive lethal test (chromosome 2) similarly showed a low sensitivity of premeiotic stages. (3) Feeding of hycanthone was much less effective than injection. This difference was not observed for the methyl analog lucanthone. From the observation that hycanthone- and lucanthone-induced mutations exhibited different germ-cell-stage sensitivity patterns, it was concluded that lucanthone does not (at least not exclusively) act via metabolic activation to hycanthone. (4) After injection, the hycanthone analogs IA-3-N-oxide and IA-4-N-oxide were marginally mutagenic. (5) It was shown previously that hycanthone was ineffective in producing breakage events, in Drosophila. In this report, hycanthone is shown to be weakly active in inducing ring-X chromosome loss. This emphasizes the relative sensitivity of the ring-X-loss test, in comparison with the tests that detect translocations or dominant lethals.