SummaryAltogether 301 haploid and 428 diploid drones originating from 33 queens were reared. More than 9500 measurements or counts were made on different reproductive organs of these drones, which were killed on their first day of adult life.The mean length of the testes of haploid drones varied from 4·61 to 5·45 mm, and the mean volume from 1016 to 14·27 mm3. Significant differences were found between different parts of reproductive organs of haploid drones originating from different queens.The testes of diploid drones are surrounded by well developed fatty tissue. The mean length of testes of diploid drones originating from different queens varied from 1·81 to 3·44 mm, and the volume from 100 to 416 mm3; the variations in diploid drones were thus much greater than in the haploids. The mean testes volume of haploid drones from a given queen was commonly 10 times as great as that of diploid drones from the same queen. The diploids had about half as many of testicular tubules as the haploids, and their vesiculae seminales and mucus glands were 85–95% the size of those of the haploids. No consistent differences were found between the sclerotized plates of the reproductive systems of haploid and diploid drones.The mean dimensions of various reproductive organs of diploid drones originating from different queens differed significantly. The small size of the testes of diploid drones, one of the factors that make it difficult to collect their semen, might therefore be ameliorated by selective breeding.