A monitoring system was used to examine the behavioral response of fathead minnows (Pimephales promelas) to plumes of the polycyclic aromatic hydrocarbon fluoranthene. Previously unexposed fish and fish surviving acute exposure to fluoranthene were presented with three different concentrations of fluoranthene. Both groups of fish avoided fluoranthene. Pre-exposure did not enhance or diminish avoidance of fluoranthene. The lowest concentration of fluoranthene which produced an avoidance response was 14.7 mu/l, and the concentration of fluoranthene which did not produce an avoidance response was 8.6 micrograms/l. These results were comparable to the LOEC for survival in 7-day fathead embryo-larval growth and survival tests for fluoranthene. Thus, a fathead minnow could escape from areas highly contaminated with fluoranthene and have a better opportunity to survive, whereas fish would fail to avoid areas where fluoranthene concentrations are below 8.6 micrograms/l and suffer further toxicosis.