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Formal kinetic methods to analyze biocatalytic systems are traditionally based on the law of mass action. This law involves the assumption that each molecular state has an exponentially distributed lifetime. We regard this assumption as unduly restrictive and advocate a more general, service theory based approach (termed mass service kinetics or, briefly, service kinetics). In service-theoretic terms biocatalysts are servers and their ligands are customers. The time intervals between arrivals of ligand molecules at special service loci (active or binding sites) as well as the service periods at these loci need not be exponentially distributed; rather, they may adopt any distribution (e.g., Erlangian, hyperexponential, variomorphic). We exemplify the impact of nonexponential time distributions on a performance measure of wide interest: the steady-state throughput. For its computation we use matrix-analytic methods. Specifically, we show that nonexponential interarrival times convert hyperbolic mass action systems (whose characteristic is a hyperbolic velocity-concentration or dose-response curve) into nonhyperbolic mass service systems and that the type and extent of their nonhyperbolicity are determined by the type and parameters of the interarrival time distribution. Furthermore, we analyze the combined effect of a non-Poissonian arrival process and a waiting site near the catalyst's active site on the throughput of the system. A major conclusion of our and other studies is that it is a questionable practice to routinely and exclusively use mass action kinetics for the interpretation and performance evaluation of biocatalytic systems. [ABSTRACT FROM AUTHOR]