Fibroblasts derived from normal dermis and keloids were cultured in nutrient medium supplemented with fetal bovine serum, serum from keloid patients, and serum from age-, sex-, and race-matched nonkeloid formers. Cell numbers were determined at various times during the growth period, and collagen synthesis was analyzed on day 7. In lag phase, keloid-derived fibroblasts were significantly reduced in all sera compared with normal dermal fibroblasts. However, beyond day 2, the growth kinetics of both cell types were similar in keloid and control human sera. Furthermore, collagen synthesis relative to total protein synthesis (percent) was similar in keloid and control human sera. Although systemic factors have been implicated in the pathogenesis of keloids and other fibrotic diseases such as scleroderma and pulmonary fibrosis, this study demonstrates that serum from keloid patients does not contain a factor(s) that significantly modifies the in vitro growth kinetics or collagen synthesis of keloid-derived or normal dermal fibroblasts.