SUMMARYMiddleton, A. L. A. 1971. The gonadal cycle of the Goldfinch in south-eastern Australia. Emu 71: 159–166. Between December 1962 and February 1965 307 male and 205 female Goldfinches were collected for gonadal study. All testes were weighed and examined histologically to provide data on the annual testicular cycle. Ovaries were not examined in histological detail, and the ovarian cycle was assessed on the measurement of the largest ovarian follicles. The seasonal change in pigmentation of the bill and the development of the brood patch were found to be reliable field criteria on which to assess the gonadal condition of living birds. The results of the study are discussed in relation to the environmental, factors which may regulate the timing of breeding.