Previously we reported an increase in bone resorption during pregnancy and lactation by measuring pyridinoline (Pyr) and deoxypyridinoline (D-Pyr). To further assess bone metabolism during peripuerperal periods, we measured the urinary excretions of C-telopeptide (CTX) and cross-linked N-telopeptide (NTX) of type I collagen, new markers of bone resorption. In addition to Pyr and D-Pyr, urinary CTX and NTX were measured by two ELISAs which recognize the corresponding peptide of type I collagen after urine samples were collected cross-sectionally from 230 women who consisted of 187 pregnants, 25 puerperants, and 18 age-matched nonpregnant women. Urinary CTX was also measured longitudinally from 10 pregnants at 5-9, 28-31 and 36-39 weeks of gestation and 1, 3, 6 months after parturition. Similar to the changes in Pyr and D-Pyr, the mean CTX and NTX values significantly increased in the 3rd trimester of pregnancy and remained high during puerperium compared with nonpregnant or early pregnant women (P<0.05). In a longitudinal study, the mean CTX value significantly increased in the 3rd trimester of pregnancy and at 1 month of puerperium compared with that in the early stage of pregnancy (P<0.05). These results further confirm our previous evidence that bone resorption is enhanced during the 3rd trimester of gestation and puerperium and suggest that urinary CTX and NTX measured by ELISA, which is more convenient than HPLC, are useful markers to assess bone resorption during peripuerperal periods.