Zebrafish pdgf-a gene was cloned and its expression pattern studied during zebrafish embryogenesis. Zebrafish pdgf-a mRNA was present at high levels in fertilized eggs as well as in all embryonic cells up to the end of gastrulation. Spatially restricted expression started after the onset of segmentation and was mainly localized in the developing pharyngeal arches. Transient expression was also detected in Kupffer's vesicle, a teleost-specific structure, and in lateral trunk and tail regions surrounding the neural keel, as well as areas of the developing pronephros.