In this study we compared bone blood flow values obtained by simultaneously injected fluorescent (FM) and radiolabeled microspheres (RM) at stepwise reduced arterial blood pressure. Ten anesthetized female New Zealand rabbits received simultaneous left ventricular injections of FM and RM at 90, 70 and 50 mmHg mean arterial blood pressure. After the experiments both kidneys and long bones of all four limbs were removed and dissected in a standardized manner. Radioactivity (corrected for decay, background and spillover) and fluorescence were determined and blood flow values were calculated. Relative blood flow estimated for each bone sample by RM and FM were significantly correlated (90mmHg: r = 0.98, Slope = 0.99, Intercept = 0.04; 70mmHg: r = 0.98, Slope = 0.94, Intercept = 0.09; 50 mmHg: r = 0.98, Slope = 0.96, Intercept = 0.07). Blood flow values (ml/min/100g) of right and left bone samples determined at the different arterial blood pressures were identical. During moderate hypotension (MAP 70 mmHg) blood flow in all bone samples remained unchanged compared to 90 mmHg, whereas a significant decrease of bone blood flow was observed at severe hypotension (MAP 50mmHg). Our results demonstrate that the FM technique is valid for measuring bone blood flow. Differences in bone blood flow during altered haemodynamic conditions can be detected reliably. In addition changes in bone blood flow during hypotension indicate that vasomotor control mechanisms as well as cardiac output play a role in setting bone blood flow.