Interleukin-6 (IL-6), produced by stromal-osteoblastic cells in response to interleukin-1 (IL-1), parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D[1,25(OH)2D], stimulates early osteoclast formation and bone resorption cooperatively with IL-1 in vivo. In adult osteoporosis, serum IL-6 is increased related to the loss of gonadal function and bone loss. Possible role of bone resorbing cytokines in rickets of prematurity has not been studied. In rickets of prematurity, we showed high serum cross-linked carboxyterminal telopeptide of type I collagen (ICTP, bon resorption marker) & osteocalcin(bone turnover marker) vs. controls; & high serum PTH & 1,25(OH)2D (Pediatr Res 35:317A, 1993). We hypothesized that serum IL-6& IL-1β would be high in preterm infants with rickets compared with infants without rickets; and bone turnover markers will be positively correlated with bone resorbing cytokines, reflecting increased osteoclastic activity by bone resorbing cytokines. Radiographic rickets was diagnosed in 17 preterm infants aged 37±12d (mean±SD) in Korea, gestational ages 30.5±1.7wks & birth weight 1333±135g. 14 controls (31.1±2.4wks; 1360±172g) had normal bone x-rays and serum biochemistry at enrollment (43±15d). Serum IL-6 & IL-1β were measured by enzyme immunoassay(Genzyme, Cambridge, MA). In rickets vs. controls, serum IL-6 concentration was similar (median with ranges; 43.5[3.91-120.1] vs. 37.8[0.82-81.3] pg/mL, p=0.9); serum IL-1β was similar (8 [2.2-59.3] vs. 7.9 [0.72-17.6] pg/mL, p=0.8). In rickets, serum ICTP was positively correlated with serum IL-1β (r=0.677, p=0.003); serum osteocalcin was negatively correlated with serum IL-6 (r=-0.846, p=0.001). Serum IL-6 or IL-1β did not correlate with serum PTH or 1,25(OH)2D. Since serum ICTP positively correlated with serum IL-1β; and serum osteocalcin negatively correlated with serum IL-6, we suggest that IL-6 and IL-1β may be involved in the high bone turnover in rickets of prematurity, but the relationships are complex.