Three inbred wildtype strains of Drosophila melanogaster, Amherst, Novosibirsk and Pacific differ in mating speed. An analysis of courtship behaviour reveals significant differences between genotypes in the latency and duration of courtship, attributable to differences in sexual response thresholds between males and levels of receptivity between females. There are significant interstrain differences in the proportions of time spent in, and bout lengths of, the principal elements of courtship behaviour of males with virgin females. Virgin females differ from fertilised females in their repertoire of courtship rejection responses and there are significant strain differences in the rates of rejection response. However, rate of rejection was not found to be a good indicator of the female's receptivity. Extrusion forms the characteristic rejection movement of fertilised females and has consequences which are genotype dependent, serving to inhibit further courtship by the male in some strains and to avoid copulation in others. Preening appears to serve as a displacement activity in males which are persistently rejected by females.