[en] The radioactive microsphere technique is tested for its applicability to the measurement of regional myocardial blood flow in the conscious baboon. Tests undertaken were: (1) the reproducibility of microsphere deposition densities, (2) recirculation of microspheres, (3) the effects of microsphere size and injection site on local microsphere depositions, (4) comparison of temporally separated injections, and (5) the effects of the statistics of microsphere distribution and of the fineness of piece-mealing on the apparent dispersion of local flows