A comprehensive evaluation of myelination during normal human development is essential to understand the pathology of congenital diseases of white matter. The present study establishes quantitative values for normal oligodendrocyte-specific gene expression during the early stages of myelination in the human fetal spinal cord. Complementary techniques of Northern and immunoblotting were used to determine relative amounts of oligodendrocyte-specific mRNAs and proteins between 12 and 24 gestational weeks. Values were determined for myelin basic protein, 2',3'-cyclic nucleotide 3'-phosphodiesterase, and proteolipid protein. The relative amount of myelin-associated glycoprotein mRNA was also estimated. To compare gene expression between glial cell types, the relative amounts of mRNA and protein were determined for glial fibrillary acidic protein (GFAP), a cell-type specific marker for astrocytes. All oligodendrocyte-specific genes expressed similar developmental kinetics. Between 12 and 15 gestational weeks, less than a five-fold increase was detected in the expression of these genes and their protein products. Between 15 and 22 gestational weeks, the relative amounts of mRNA and protein for the myelin genes increased more than 80-fold. The kinetics of GFAP expression were similar to those of the myelin-associated genes. Absolute values for the increase in mass of the human fetal spinal cord were also obtained. These results provide data that may aid in the neuropathologic assessment and characterization of myelin disorders in the preterm, neonatal, and pediatric spinal cord.