Oestrus, ovulation and peripheral plasma progesterone concentrations were recorded in 58 lactating South African Mutton Merino ewes treated variously with progestagen, pregnant mare serum gonadotrophin (PMSG), prostaglandin and gonodotrophin releasing hormone (GnRH) at 2 post partum intervals (22 or 35 days post partum) during the non-breeding season. Ovulation was induced in 46 % ewes, with no significant variation between 6 different hormone treatments. Only 7 ewes (78 %), all treated with progestagen and PMSG, were detected in oestrus. Plasma progesterone levels in ewes treated with progestagen and PMS were similar to those reported for spontaneous oestrous cycles in non-lactating ewes. Ewes treated with progestagen between 2 spaced injections of PMSG showed a normal duration of progesterone production, but reduced peak concentration, viz. (1,40 ng/ml). A high proportion of ewes treated with PMSG alone (60%) or GnRH alone (70%) showed subnormal peak progesterone concentrations and shortened periods of elevated plasma progesterone. This subnormal progesterone production was not counteracted by twice-daily injections of PMSG for 16 days after GnRH injection. Prostaglandin appeared to have no lutcolytic effect in some ewes in which functional corpora lutea had been induced by PMSG injection.