The objective of this cross-sectional study was to determine whether habitual physical activity such as daily walking at work affects bone mineral density (BMD) in healthy premenopausal women. Thirty-one letter or newspaper carriers and 30 sedentary (non-exercising) office workers were screened out from 167 subjects working in the public post office and a private newspaper publishing company. BMD was measured with a dual-energy X-ray densitometer at the lumbar spine (L2-4), femoral neck, distal femur, patella, proximal tibia, calcaneus and distal radius. In addition, maximal isometric strength, cardiorespiratory fitness, anthropometry, 4-day dietary record and daily occupational work load were assessed. During one work shift the carriers' mean walking distance was 5926 m, with 68 flights of stairs walked, and their mean heart rate was 105 beats/min (114 beats/min during the delivery). The corresponding figures for the office workers were significantly lower: 1895 m, 10 flights and 82 beats/min, respectively. Neither the BMD values adjusted for body mass index (kg/m2) and calcium intake nor the indices of physical performance capacity showed significant differences between the groups. Consequently, habitual daily walking and stair climbing by healthy premenopausal women appeared to be insufficient exercise stimulus to increase considerably the BMD or aerobic and muscular fitness above the values found in a comparable group of sedentary office workers.