The fatty acid composition of the ethanolamine and choline phosphoglycerides was examined in the testes of Merino sheep aged 2� 5 years and lambs aged 2 weeks, and Large White crossbred pigs aged 3 years and young pigs aged 5 months. Only in the case of the choline phosphoglycerides was there a noticeable increase in the polyunsaturated fatty acid content with maturation, but the ethanolamine phosphoglycerides contained higher levels of polyunsaturated fatty acids throughout. Sheep testes were characterized by the absence of 4,7,1O,13,16-docosapentaenoic acid, but contained high levels of 4,7,1O,13,16,19-docosahexaenoic acid, particularly in the ethanolamine phosphoglycerides. This latter acid was also evident in the pig testes, but derivatives of linoleic acid, particularly arachidonic and 4,7,10,1 3, I 6-docosapentaenoic acids, were dominant.