Several factors influencing the apparent phytodegradation of pentachlorophenol (PCP) were investigated under controlled laboratory conditions including photolysis, biodegradation, and direct phytodegradation by the algae, Chlorella pyrenoidosa. PCP was observed to degrade over time in all instances. Degradation occurred both with and without the presence of algae. The degradation of PCP was observed to be dependent primarily on photolysis with pseudo-first-order kinetics and rate constants in the range of 6.4 to 7.7 h(-1). In contrast, phytodegradation due to algal activity was negligible. It is suspected that the algae degradation may have been limited by the cycling of light exposure to simulate day and night periods.