Concentrations of immunoglobulin G (IgG) were determined in periparturient llamas, alpacas and their crias for up to 60 days of age. Mammary secretion was collected before and after parturition. Serum samples from pregnant animals and their crias were collected by jugular venipuncture. Concentrations of IgG were determined by radial immuno diffusion test. Concentrations of IgG in sera of periparturient llamas (mean 3098.2 mg dl-1) were not different (P > 0.05) from alpacas (3126.1 mg dl-1) throughout the study period. Concentrations of IgG in mammary secretion were different (P < 0.05) throughout the study period with mean values being 23698.8 mg dl-1 before parturition, 19261.9 mg dl-1 at day of parturition, and 9174.3 mg dl-1, 5656.1 mg dl-1, 2896.1 mg dl-1, 2103.5 mg dl-1, 1385.1 mg dl-1, and 633.7 mg dl-1, for 1, 2, 3, 4, 5, and 6 days after parturition, respectively. Mean concentrations of IgG in sera of crias were different by days (P < 0.05) with 0 mg dl-1, 2342.9 mg dl-1, 2329.2 mg dl-1, 3201.2 mg dl-1, 2738.1 mg dl-1 and 2638.8 mg dl-1 at time of birth, 12 h, 1, 2, 3, and 4 days after birth. There was no difference (P > 0.05) in mean IgG concentrations between species, llama (2370.6) and alpaca crias (2347.1), and no difference (P > 0.05) in general mean values between male (2342.3) and female (2352.2) crias. Concentrations of IgG in sera of pregnant females were maintained unchanged; however, changes did occur after parturition in mammary secretions. Llama and alpaca crias were born agammaglobulinemic with IgG concentrations increasing rapidly after suckling. © Published by 1997 Elsevier Science B.V.