Aspects of the metabolism and passive transfer of radioactive 125I-labeled IgG, IgM, and IgA from the turkey hen to the egg were studied. The half-life of 125I-labeled IgG in plasma was calculated to be 5.91 +/- 0.81 days, and the time of maximal passage of radioactivity from hen into eggs was 6.5 +/- 1.3 days. The following IgG determinations were made: plasma concentration (8.54 +/- 1.2 mg/ml), total plasma pool (0.518 +/- 0.07 g/kg), total turnover rate (0.062 +/- 0.01 g/kg/day), or 11.92 +/- 0.01% of the plasma pool per day. The overall passage of IgG into sequentially laid eggs of individual hens was at a constant rate over an observation period of 46 days; loss to egg yolks accounts for less than 1% of total daily irreversible loss of IgG from the hen's body. The IgG concentrations in egg yolks assayed in 3 hens ranged from 72.1 +/- 6.7 to 104.5 +/- 6.9 mg/yolk, with significant (P less than or equal to 0.01) differences observed between birds not accounted for by differences in egg weights. The IgG was detectable in egg whites, but at a low concentration. The biological importance of egg white IgG is questionable. In 2 hens examined, 125I-labeled IgM had a half-life of 2.69 and 2.74 days, with fractional turnovers of 25.76% and 25.29% of the plasma pool/day. The IgM-associated radioactivity in egg material was considered unimportant in overall immunoglobulin transfer into eggs. In 2 hens examined, 125I-labeled IgA (biliary) had a half-life of 1.92 and 1.68 days, with fractional turnovers of 36.09% and 41.25% of the plasma pool per day. Like IgM, IgA-associated radioactivity in egg material was considered unimportant in overall immunoglobulin passage into eggs.