PMS was injected thrice weekly for four weeks into first winter and second winter canaries during the following periods: September-October, November-December, January-February and February-March. Measures were made of ovary and oviduct weight, brood-patch development (defeathering, vascularity and sensitivity changes), nest-building and egg-laying. PMS caused overy growth in all months: this was greatest in the second year birds in February. Both control and treated ovaries increased in size towards the breeding season. Oviduct growth depends mainly on the size of the treated ovary. Defeathering was produced by PMS in all months: its rate and extent increased towards the breeding season. Vascularity was also produced by PMS. It was least in November-December but after that the rate at which it appeared increased towards the breeding season. By contrast, the effect of PMS on brood-patch skin sensitivity was greater in the autumn group than subsequently. Nest-building occurred in September-October, but was then very slight until February-March, which is the beginning of the breeding season. Eggs were laid in most months; fewer injections were needed to produce egg-laying as the breeding season approached.