Although these two hypotheses imply different causal mechanisms, it has been difficult to adjudicate between them, in part because of data and methods employed in prior research. The current study investigated whether a large increase in jail capacity in Orange County, Florida, increased daily jail incarceration rates above those expected on the basis of pre- existing incarceration trends and police activity. Data were obtained for a 1-year period between July 1991 and June 1992. Results were consistent with the hypothesis that available capacity influenced incarceration rates. The number of daily arrests made by police, however, was of little consequence in predicting incarceration rates. Findings suggest that adding additional capacity may accelerate the growth of the confinement population. Theoretical and policy implications of the findings are discussed. 28 references, 7 notes, 2 tables, and 1 figure