Laboratory studies have shown that people cannot handle the time con-stants in dynamic tasks. Yet they obviously cope with such tasks with some success outside the laboratory. This study is one in a series of studies that examine the hypothesis that people cope by relying on heuristics that allow them to simplify the task. The heuristic studied here was that of relying on frequency differences, i.e., what Reason (1990) calls frequency gambling. It examines the effects of varying the relative frequency of scenarios that require different responding, and where relying on frequency rather than learning the actual time con-stants will lead to some success. The results show that the participants did not learn the time constants, that frequency had a strong effect on their decisions, but that their responding also seemed to be influenced by another heuristic identified in earlier studies, viz., that of rapid and massive responding. Implications of these findings for system dynamics modellers are discussed.