Patients with growth hormone (GH) deficiency (GHD) have a clinical feature of visceral adiposity and it has been reported that these patients have an increased active cortisol (F)/inactive cortisone (E) metabolite ratio. 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is an enzyme expressed in liver and adipose tissue that acts principally as a reductase converting E to F. In the present study, we investigated the effects of GH or IGF-I on the activity of 11beta- HSD1 in 3T3-L1 cell homogenates and its mRNA expression. First, we showed that 11beta-HSD1 activity and mRNA levels were low in preadipocytes and increased throughout the process of adipogenesis. When fully differentiated adipocytes were treated with GH for various times, the activity of 11beta-HSD1 was significantly decreased after 4 h and 8 h but was restored to basal levels after 24 h. After 8 h of GH stimulation, 11beta-HSD1 mRNA levels were decreased compared with basal levels. IGF-I treatment of adipocytes resulted in rapid decreases in 11beta-HSD1 activity as well as mRNA levels; however, IGF-I treatment for 24 h increased 11beta-HSD1 activity. In long-term cultured adipocytes, GH or IGF-I showed only inhibitory effects on 11beta-HSD1 activity. In conclusion, 11beta-HSD1 activity was suppressed by GH or IGF-I in differentiated adipocytes, probably due to a reduction of 11beta-HSD1 mRNA levels. These data suggest that under the conditions of low GH or IGF-I concentrations, 11beta-HSD1 activity in adipose tissue is maintained at high levels, leading to an increase in active cortisol that induces adipogenesis and/or lipogenesis. Thus, visceral adiposity in patients with GHD might be related to increased 11beta-HSD1 activity.