The stimulatory effect of recombinant basic fibroblast growth factor (bFGF) on wound healing was assessed using healing-impaired (db/db) mice. Full-thickness wounds were made in female diabetic C57BL/KsJ db/db mice, and their normal (db/+) littermates with a punch biopsy instrument. Recombinant bFGF was applied locally to the open wound once a day. The mice were later killed and histological sections of the wounds were prepared. The degree of wound healing was evaluated using several histological parameters such as degree of reepithelialization, granulation tissue thickness, matrix density, number of infiltrated cells, and number of capillaries. Wounds from normal mice displayed good reepithelialization rates and granulation tissue formation, while wounds from db/db mice had poor responses, especially in the dermal parameters. Although the application of bFGF to wounds in the normal (db/+) mice had little effect, application of bFGF to wounds in db/db mice induced significant responses in all of the dermal parameters compared with nontreated db/db mice (p less than 0.001). In the presence of bFGF, these parameters approximated those observed in nontreated littermates. A minimum of 0.5 microgram bFGF in either single or multiple applications was required for a significant effect. bFGF that was either boiled or pretreated with neutralizing antibody had little stimulatory effect. Time-course experiments indicated that the granulation response in bFGF-treated mice peaked between 8 and 12 d, and decreased after 12 d, while matrix density continued to increase until the 18th day (p less than 0.05). The breaking strength of healed linear wounds in db/db mice was also decreased when compared with heterozygous littermates. This parameter was also improved by the administration of bFGF to the wounds (p less than 0.05).