Blood was collected from 28 zebra mares (Equus burchellia antiquorum) immediately after being shot in the .Kruger National Park. The serum was separated within two hours after collection and then stored at -15°C for later assay. Of these, thirteen selected samples were tested for gonadotrophic activity. The stage of pregnancy was determined from a foetal growth curve. Blood samples from pregnant horse mares were collected by venipuncture. Nine mares were sampled. Seven blood samples at different stages of pregnancy were collected from one mare, four from another and only one sample each from the other seven mares. The stage of pregnancy was calculated from the date of last service.