A diallel cross inDrosophila melanogaster for the mating speeds of previously unmated pairs aged 6 days was carried out for 6 inbred lines and their hybrids. Pairs were observed for 40 minutes. There was extreme hybrid vigour especially in mating frequency for ≤10 minutes but the degree of hybrid vigour was relatively smaller for ≤40 minutes. Considerable variability occurred between the inbred lines indicating the genotypic control of mating speed. An analysis of variance on the hybrids revealed significant general and specific combining abilities, and reciprocal effects. The mating frequency for ≤10 minutes gave heritability in the narrow sense, h2=0.605, ≤20 minutes gave h2=0.510 and ≤40 minutes gave h2=0.342. The progressive reduction in h2 is due to a decrease in additive genetic variance and an increase in dominance variance with time. Thus either the dominance relations of genes controlling mating speeds change with time. or different loci control this character at different times.