The occurrence of monoclonal gammopathy in childhood is extremely rare. This report describes the presence of a monoclonal immunoglobulin in a 30 week old premature infant, incidentally discovered by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) during an ongoing study of the plasma/serum protein development. Comparative analysis of the electrophoretogram of the infant with 'reference' protein maps revealed the presence of an 'abnormal' immunoglobulin light chain spot. A spot having an identical apparent molecular weight and isoelectric point was also detected after 2D-PAGE of the mother's plasma and its Protein-A purified immunoglobulin fraction. The observation of a monoclonal gammopathy in a premature infant, most likely transmitted from his mother, highlights the potential usefulness of 2D-PAGE in the clinical laboratory.