Biochemical variation at 14 blood loci was reviewed, and specific features compared experimentally in sheep Ovis aries, mouflon Ovis mwimon, goat Capra hircus, aoudad Ammotragus lervia and in 2 stillborn aoudad X goat hybrids. Variation at 3 loci was also studied in dall sheep Ovis dalli, bighorn sheep Ovis canadensis and rocky mountain goat Oreamnos americanus. Haemoglobin C production in an anaemic Hb AB mouflon and in mouflon X sheep hybrids was examined. Mouflon differ from domestic sheep in that synthesis of both H b ,&I and H b BB chains is switched off during Hb C production. The mouflon X sheep hybrids switched off one or both chains depending on whether they had inherited sheep or mouflon Hb , 8 chain genes. In general aoudad showed a closer affinity to goats than to sheep.