A technique based on the stochastic method is described for the computation of regional blood flow (RBF) after intra-arterial infection of 133Xe. Results are presented on scintigrams, defined by 600-800 channels in a 64 times 64 matrix. The content of each channel is equal to the computed RBF value. The standard deviation is also computed for each channel. The total computation cycle is achieved within 10 min. The method has been used to investigate the influence of anesthesia or drugs on regional blood flow. For this purpose, a differential printout program was written in which variations of RBF values between the two measurements are expressed in units of a fixed percentage; provision is made for calculation of RBF variations in units of differential standard deviations. Data are in good accordance with other clinical findings. This method is suitable for clinical use when blood flow values in gray and white substances are not requested.