We studied the spatial and temporal pattern of basic fibroblast growth factor (bFGF) immunoreactivity in the rat adrenal gland during postnatal development. In the cortex the glomerulosa zone reveals a strong anti-bFGF immunoreactivity at all developmental ages studied. In the fasciculata zone the high number of anti-bFGF immunoreactive cells in the first week decreases during the second and third week. The late developing reticularis zone shows only few anti-bFGF labeled cells at all postnatal ages. This distributional pattern of bFGF immunoreactivity matches that of mitotic activity in the rat adrenal cortex strengthening the role of bFGF as an autocrine growth factor for adrenocortical cells. In the medulla anti-bFGF positive chromaffin cells become detectable at postnatal day (P) 8 and increase in number during the second and third week. In the adult rat the staining intensity of the chromaffin cells was higher than at P18. In the adult medulla bFGF colocalizes with noradrenaline suggesting its presence in a chromaffin cell subpopulation. In accordance with previous results the role of the chromaffin cell bFGF as a neurotrophic factor for preganglionic sympathetic neurons is discussed.