Soluble leptin receptor is an extracellular domain of the leptin receptor that serves as the main leptin-binding protein and may play a role in the regulation of leptin tissue effects. The aim of our study was to assess serum concentrations of leptin, soluble leptin receptor, and other hormones involved in the regulation of leptin secretion in pregnant women before and after delivery. Serum leptin, cortisol, and tumor necrosis factor alpha (TNF-alpha) concentrations in 19 pregnant women before delivery were significantly higher than in healthy nonpregnant women (33.3+/-21.0 vs. 7.9+/-3.5 ng/mL, 1068.9+/-442.2 vs. 546.6+/-165.3 nmol/L, 4.4+/-1.1 vs. 3.4+/-1.2 ng/mL, respectively). In contrast, no differences between these groups were found in soluble leptin receptor levels. Delivery significantly decreased serum leptin and cortisol levels and increased soluble leptin receptor levels (12.3+/-9.1 ng/mL, 749.6+/-205.3 nmol/L, 23.3+/-7.9 U/mL, respectively). Soluble leptin receptor levels after delivery became higher than in the control group. We conclude that serum leptin and serum soluble leptin-receptor levels are significantly affected by pregnancy and delivery. The regulation of leptin levels in this group of patients appears to be distinct and independent of soluble leptin-receptor levels.