We have quantified the levels of IgG, IgA and IgM in Nigerian cord blood samples during the dry and the wet seasons. Almost all the samples collected during both seasons had detectable levels of IgG and IgM, while IgA was detected in 71% of those collected in the rainy season and in only 45% of those collected during the dry season. We observed seasonal variations in the levels of each of these immunoglobulins but the variations were not consistent for all three immunoglobulin classes. This suggests that the levels of each immunoglobulin class in the cord blood is probably controlled by different antigenic factors in our environment. The mean values for all three immunoglobulin classes were raised in all our samples above those of UK cord blood samples. This is consistent with earlier reports for samples collected in the tropics. In the paired cord/maternal immunoglobulin estimations, 75% of cord sera had higher levels of IgG than their corresponding maternal samples, suggesting either active transfer of the immunoglobulin across the placenta or increased rate of synthesis or decreased rate of catabolism in utero.