Sexually mature New Zealand White male rabbits were subjected to various sexual stimulation procedures. Plasma samples were obtained through an indwelling catheter in the central ear artery and analysed for LH and testosterone using specific radioimmunoassays. Coitus and exposure to females occasionally led to increases in testosterone levels which were usually preceded by a rise in LH. Increases in hormone concentration were not significantly different from those of rabbits which did not mate or which were isolated from females. These results suggest that coitus in the male rabbit does not cause the massive increase in LH concentration which is known to occur in the female.