Four proteins immunologically related to basic fibroblast growth factor (bFGF) have been detected by Western blot analysis in the extract from rat anterior pituitary. Their apparent molecular weights are 29, 27, 18, and 14 kDa, respectively. A similar immunoreactive pattern has been observed in the rat tumor pituitary GH3 cell line. In the extracts from rat neurohypophysis, hypothalamus, hippocampus, striatum, olfactory tubercles, cerebellum, and cortex only the 29 kDa form is detectable in a significant amount.