The correlation between intensity of Ancylostoma caninum infections in bitches and the intensity of lactogenic infections and clinical signs of their puppies was investigated. On average, 825, 1,867 or 2,125 specimens were observed in litters of two bitches inoculated with 5,000, 10,000 or 20,000 third stage larvae (LIII) respectively, at the day of conception. Adverse effects of the infection on the growth and behaviour of the puppies were observed after onset of their second week of life: 11/27 puppies died during the fourth week. The body weight of puppies surviving 28 days was up to 750 g less than that of uninfected controls. Eosinophilia, erythroblastosis and microcytic, hypochromic anemia developed in all puppies during their first four weeks. The IFA test (LIII antigen) was positive for only 5/18 heavily infected puppies after uptake of colostrum.