We report on an experimental investigation of sofrware reliability data. Our hypothesis in this investigation is that sofrware failures are the result of a findamentally deterministic process, rather than being realizations of a stochastic process as is commonly assumed. Using the techniques of nonlinear time series analysis, we examine three sofhvare reliability datasets for the signatures of deterministic, and possibly chaotic, behavior. In these datasets, we have foundfirm evidence of

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... nistic behavior, and hints of chaotic behavior. However, the latter are too limited to permit a definitive conclusion about the presence or absence of chaotic behavior.