In vitro effects of bFGF on neural tube, heart, and total embryonic development were investigated in 60 rat embryos (obtained from seven pregnant females) at 9.5 days of gestation that were cultured in whole rat serum (WRS), in >30 kDa serum fractions [retenate (R)], and in R+bFGF. After 48 h culture, the embryos from each group were harvested and divided into two groups. One group was analysed morphologically and biochemically to obtain embryo protein content, the second group was serially sectioned and examined by light microscopy. Morphological score, embryo protein content, somite number and crown-rump length of embryos indicated that embryos cultured in R had significant embryonic retardation, whereas the addition of bFGF to R increased embryonic growth and development. The morphological scores for WRS, R and R+bFGF were 57.7+/-0.87, 46.6+/-1.90 and 52.1+/-0.97, somite numbers were 26.5+/-0.47, 20.1+/-0.63 and 24.4+/-0.46, crown-rump lengths were 3+/-0.07, 2.4+/-0.06 and 2.7+/-0.06 mm, and embryo protein contents were 160.5+/-7.41, 98.2+/-4.81 and 141.1+/-10.96 mg per embryo, respectively. The results of histological examination showed that the hearts of embryos grown in R were unseptated and tubular. These embryos also have open cranial and caudal neural tube defects. The addition of bFGF to R improved heart development. In WRS and R+bFGF groups, development of the muscular interventricular septum had begun. Both the morphological analyse and histological sections showed that the bFGF caused improved growth in heart and neural tube formation.