Bone loss is uniformly observed from immobilised limbs, e.g. after spinal cord injury, during space flight, and during bed rest. The latter is an accepted model for ground based microgravity research. Unilateral lower limb suspension (ULLS) is a new alternative to such bed rest studies (1), evoking a muscular atrophy which is comparable to that observed during bed rest. To the best of our knowledge, bone loss during ULLS has never been demonstrated before. However, there might be reason to assume that bone loss does not occur during ULLS. According to studies both in animals and in humans, an increase in interstitial fluid pressure seems to hamper the bone loss induced by immobilisation. However, we hypothesized that bone loss during ULLS does occur, and that it does so to an extent that is comparable to bed rest. Eight young healthy volunteers participated in a ULLS study. Their mean age was 19 years (SD 0.76), their height was 179.3 cm (SD 4.7) and their mean body mass 72.4k g (SD 8.6). Their right leg was suspended for 24 days, using a strap to tie it so the knee angle was 10 deg whilst using crutches with both hands and a 7.5 cm sole under their left shoe. Bone scans from both lower legs were obtained by peripheral Quantitative Computed Tomography (pQCT) with an XCT 2000 (Stratec Medizintechnik, Pforzheim, Germany). Measurements were performed during baseline data collection (two times), on days 7, 14 and 21 of the ULS, and on days 4, 9, 35 and 90 of the recovery. Bone mineral content (BMC) of the distal tibia (at 4% of its length) was assessed with the integrated XCT 2000 software version 5.40. A repeated measure ANOVA design with simple a-priori contrasts was used to detect a time effect. For the distal tibia epiphysis of the suspended leg, a significant time effect was found (p = 0.001). The bone loss became significant on day 4 of the recovery (p = 0.016). It was largest on day 35 of the recovery, when it amounted to 1.09% (p = 0.009, SD 0.68). No significant loss was observed from the left tibia. For the first time, bone loss has been observed during a limb suspension study in humans. This fills a gap in the scientific literature, as limb suspension is a model which is often used to study the effects of immobilisation on bone in rats. As the limb suspension in this study was comparatively short for a study of bone, the present data do not allow for a definitive assessment of the rate of bone loss. However, a comparison with data from bed rest studies (2) suggests that the rate of bone loss may be comparable in bed rest and in ULLS. If this were to be substantiated in a future study with limb suspension over a longer period, then that would constitute strong evidence against a decisive role of interstitial fluid pressure for immobilisation induced bone loss.