Lymphocytes and monocytes in human cord blood have been analysed using a panel of fourteen monoclonal antibodies. Contrary to earlier data based on the sheep erythrocyte rosette assay for T cells, no marked deficit in T cells was found in cord as compared with adult blood. The T cells in cord blood had a relatively immature phenotype whereas B cells showed a mature phenotype. The phenotypic differences between adult and cord blood appear minor in relation to the marked functional differences reported by others.