Two types of nest building are found in the rabbit. One type of nest is made of straw or similar elements available to the animal, and a second type of nest is composed of straw into which hair is incorporated after being plucked from the body. The second type of nest is called a maternal nest and is considered to be part of the maternal behaviour complex. Maternal-nest building was induced in 209 out of 250 (84 %) rabbits following complete removal of the entire conceptus mass on Days 20 to 27 of gestation, as compared with a 96 % maternal-nest-building rate in 941 control rabbits from the same colony. The maternal-nest-building behaviour was also induced in twelve out of sixteen (75 %) rabbits following ovariectomy on Days 20 to 24 of gestation and in five out of eleven rabbits made pseudopregnant with human chorionic gonadotrophin (hcg). Comparable results were obtained in a separate study that used the Dutch-belted rabbit, although a higher percentage of animals in this race built maternal nests following pseudopregnancy or ovariectomy during gestation. Treatment with stilboestrol, progesterone and prolactin induced maternal-nest building in four out of seventeen rabbits and lactation in all the animals. Possible endocrine mechanisms involved are discussed.