[en] Three experiments were conducted in which Drosophila melanogaster males were labeled with (5-³H)-deoxycytidine, (8-³H)-deoxyguanosine, or L-(3-³H)-arginine in the larval stage. In the first two experiments with 5-³H-dC and 8-³H-dG, the labeled males upon eclosion were divided into two groups: 1) those mated to females that from emergence as adults were sustained on a media deficient in protein, called sugar agar media; and 2) those mated to females that were on a standard nutritious media. All males from the arginine experiment were mated to females stored on the standard media. The labeled males were allowed to mate for two days during which time the females stored on standard media deposited fertile eggs. Those F₁ progenies developing from the brood of eggs laid during the first 48 hrs following mating were called the non-stored group, as the spermatozoa were not stored in the female for more than 48 hrs. Progenies of males that were mated to females sustained on the sugar agar media were referred to as the stored group because the females on the sugar agar did not lay eggs. After 14 days the females were transferred to regular corn meal agar to induce egg laying. The average time of storage of sperm in the females' seminal receptacles for the stored group was 18 days. The progenies from the non-stored and stored broods were analyzed for mutations thus giving a comparison of the mutation frequency for each class of mutants detected before and after storage of the tritium-labeled sperm. The difference between the mutation frequency following storage and that before storage is the increase in mutations attributed to tritium disintegrations occurring during the storage period. One determination for each experiment, 5-³H-dC, 8-³H-dG, or ³H-Arg. has been made