The effects of a high protein diet (casein 40%, lactalbumin 20%) were evaluated in pregnant and/or suckling rats. Histological studies of the organs showed structural alterations to the liver, adrenal cortex, kidneys and heart accompanied by significant metabolic changes in blood glucose and triglyceride levels. Overall the experimental results encourage the belief excessive intake of animal protein, particularly at an early stage, may do specific damage to the normal course of pregnancies, given the low birth rate and high incidence of perinatal mortality observed in the offspring produced by mothers given high protein diets throughout pregnancy.