Cycloheximide, an antibiotic inhibiting protein synthesis, exerted a toxic effect on different developmental stages egg, larva and adult of Drosophila melanogaster. At the egg stage the early embryos were most sensitive. With larvae, a strong decrease in viability was found, with no sex difference. In adults, there was a dose-effect relationship, mortality increasing with concentration. At 10 and 15 mM, males were more sensitive than females. There were consistent differences between the control and cycloheximide-fed females in respect of the average number of eggs deposited and offspring produced. © 1982.