PC BEEPOP is a computer model that simulates honey bee (Apis mellifera L.) colony population dynamics. The model consists of a feedback system of interdependent elements, including colony condition (e.g., initial size, reproductive potential of the queen and forager longevity), environmental variability (e.g., weather) and contaminant exposures. It includes a mortality module (BEEKILL) and a chemical-toxicity data base and probit analysis program (BEETOX). PC BEEPOP is a modified version of an cxisting colony dynamics model, BEEPOP, and can be used as a tool for environmental risk assessments. Results of sensitivity analysis and simulations of various climatic and toxic scenarios are discussed and compared to observed changes in the size and composition of honey bee colony populations.