The distribution of cell-surface 04 antigen and galactocerebroside (GC) was examined by dual-label indirect immunofluorescence assays on live primary cultures of human spinal cord cells dissociated from 8-12 week-old foetal tissue. Oligodendrocytes expressing GC on their surface were present in the cultures at early time points, and all GC-positive cells were found to also express cell-surface 04 antigen. The 04 antigen was found additionally on a further population of GC-negative cells in the spinal cord cultures, which did not react with antibodies to glial fibrillary acidic protein (GFAP), and were distinct from neuronal cells and cell processes which stained with anti-neurofilament antibody. Previous studies in mouse neural cell cultures have shown that 04 antigen-positive cells are direct precursors to GC-bearing oligodendrocytes (Schachner et al. 1982). In the human spinal cord cultures, a rapid decline in the number of cells expressing GC and/or the 04 antigen to a value below 1% was observed during the first 3 days in vitro. The present studies indicate that synthesis of GC occurs in the human spinal cord many weeks before myelination commences in vivo and that GC-negative oligodendrocyte precursors are present simultaneously with more mature GC-positive cells. In addition, it would appear that complex humoral or cellular ingredients may be required for the long-term in vitro maintenance of viable human foetal oligodendrocytes.