We examined neonatal lymphocyte production of the lymphokine, lymphocyte-derived chemotactic factor (LDCF). Supernatants from 10 neonatal lymphocyte cultures were paired with the supernatants from 10 adult lymphocyte cultures. Chemotactic activity was defined as the number of adult monocytes migrating toward phytohemagglutinin-stimulated supernatants minus the number of monocytes migrating toward nonstimulated control supernatants using a blind well chamber assay. Eight of the 10 neonatal lymphocyte cultures produced LDCF and five of the 10 adult lymphocyte cultures showed LDCF activity. The mean number of monocytes migrating toward neonatal supernatants was 13.0 ± 1.5 and toward adult supernatants was 14.1 ± 2.1. To determine if a quantitative difference in LDCF production did exist, six additional experiments were performed assaying multiple dilutions of supernatants. No evidence was found for a quantitative difference in neonatal LDCF production compared to adult production. Our studies show that neonatal mononuclear cells are functionally as competent as adult mononuclear cells to produce LDCF in response to a mitogen challenge.