Summary Teat ligation of 3 abdominal-inguinal mammary glands of lactating rats markedly decreased DNA and RNA content and RNA/DNA ratio when compared with similar estimates of either contralateral, non-ligated glands or glands from normal rats lactating the same length of time. Suckling stimulus, without milk removal, did not prevent cellular loss and did not maintain level of protein synthesis. DNA and RNA content and RNA/DNA ratio of contralateral, non-ligated glands were greater than those of glands of normal rats lactating comparable periods of time.