We describe a new technique for the analysis of dynamic positron emission tomography (PET) studies in humans, where data consist of the time courses of label in tissue regions of interest and in arterial blood, following the administration of radiolabelled tracers. The technique produces a simple spectrum of the kinetic components which relate the tissue's response to the blood activity curve. From this summary of the kinetic components, the tissue's unit impulse response can be derived. The convolution of the arterial input function with the derived unit impulse response function gives the curve of best fit to the observed tissue data. The analysis makes no a priori assumptions regarding the number of compartments or components required to describe the time course of label in the tissue. Rather, it is based on a general linear model, presented here in a formulation compatible with its solution using standard computer algorithms. Its application is illustrated with reference to cerebral blood flow, glucose utilization, and ligand binding. The interpretation of the spectra, and of the tissue unit impulse response functions, are discussed in terms of vascular components, unidirectional clearance of tracer by the tissue, and reversible and irreversible phenomena. The significance of the number of components which can be identified within a given datum set is also discussed. The technique facilitates the interpretation of dynamic PET data and simplifies comparisons between regions and between subjects.