Immunogen: Recombinant human ectodomain of FGFr1a expressed in E. coli beginning with pro23; antigen contained NH2-terminal gly-ser-pro-gly-ile and COOH-terminal glu-phe sequences. Epitope: NH2-terminus of unique NH2-terminal Ig loop of FGFr1. Epitope is within the sequence between glu30 and ala74 of FGFr1a.