MIC-II is a versatile BASIC computer program designed to calculate the cardiac output, the arterio-venous shunt and the regional blood flow from data obtained by the radioactive microsphere method. The samples are measured in a gammaspectrometer with a multichannel pulse height analyzer and the data are recorded on tape. Up to 10 different nuclides may be used simultaneously, including tracers which are not bound to microspheres. The nuclides may have overlapping energy spectra. The analysis of the energy spectra is performed according to the matrix method. Standard samples, each containing one pure nuclide, are measured to obtained the overlap matrix. The unkown amounts of the nuclides in the samples are obtained by solving a system of simultaneous linear equations. Up to 100 organ samples may be taken in one experiment. Up to 10 different organ maps, containing a text label for each organ specimen, may be created, edited, modified and stored on tape for convenient identification of input and output. Numerous validity checks for imput and output make MIC-II easy to use, even for non-computer trained personel.