Twenty-five ferret jills were randomly allocated to five groups of five animals; they were treated either before the breeding season with 15 mg medroxyprogesterone acetate (MPA), with 40 mg proligestone or with a slow-releasing device containing 4.7 mg of the gonadotropin-releasing hormone (GnRH) agonist deslorelin acetate (srGnRH), or at spring oestrus with 100 iu human chorionic gonadotropin (hCG), or were left untreated and mated. All the ferrets were assessed for signs of oestrus and their ovarian response was monitored by individual faecal progesterone metabolite (P4-met) profiles. The mean (sd) durations of treatment-induced ovarian quiescence were 94 (18), 99 (40), 53 (9) and 698 (122) days in the group treated with MPA, proligestone, hCG and srGnRH, respectively (P<0.001). Treatment with hCG and srGnRH proved to be the safest, while MPA treatment was associated with most side effects. Both MPA and proligestone treatments caused alopecia in one ferret per group, and after the first return to oestrus and mating an MPA-treated jill had a premature delivery and developed a purulent vaginal discharge. At the first post-treatment mating, the fertility (expressed as the percentage of ferrets mated in the group that produced a litter) was 75 per cent in the MPA-treated group, 60 per cent in the proligestone-treated group, 75 per cent in the hCG-treated group and 0 per cent in the srGnRH-treated group; in the control group, fertility was 100 per cent at mating in spring and 60 per cent at mating in summer. Three srGnRH-treated jills conceived at the second post-treatment oestrus.