The relationship between past and present lifestyle and urinary excretion of type I collagen cross-linked N-telopeptides (NTx) was studied in 61 Japanese females aged 34-59, with a view toward using NTx excretion rates as a predictor of future osteoporosis. Bone mineral density (BMD) of the lumbar spine, the speed of sound (SOS) and broadband ultrasound attenuation (BUA) of the os calcis, urinary NTx, serum osteocalcin (BGP) and bone-specific alkaline phosphatase (BAP) were measured. Stiffness index (stiffness) was calculated from SOS and BUA. The subjects were asked whether they took regular exercise in their childhood and teen years (in elementary, junior-high, senior-high school and college), the past (20-40 years of age) and present adulthood. Regular calcium intake, smoking habits, alcohol and other beverage consumption and milk consumption were also covered in the questionnaire. The mean NTx values of premenopausal and postmenopausal group were 22.2 and 56.0 nM bone collagen equivalents (BCE)/mM urinary creatinine (Cr), respectively. The group which did not exercise regularly between the ages of 20 and 40 had a higher mean NTx value (40.9 nMBCE/mMCr) than the group which did exercise regularly (22.7 nMBCE/mMCr). In multiple regression analyses, age, stiffness and exercise in past adulthood could explain 43.5% of the NTx variance. For prevention of bone metabolic increases around menopause, habitual exercise in early adulthood seems to be effective.