The effect of 2,4-dichlorophenol on the growth of Chlorella VT-1 has been studied. 2,4-Dichlorophenol at concentrations of 10-30 mg/l inhibited the initial growth of Chlorella VT-1 with an LD50 of 22.5 mg/l. The higher the concentration of 2,4-dichlorophenol, the longer the lag phase was but when growth resumed it was at a rate similar to that of the control culture. 2,4-Dichlorophenol inhibited both respiration and photosynthesis and this inhibition could be avoided by the addition of glutathione. HPLC analysis indicated that 2,4-dichlorophenol was removed from the culture medium but no degradation products were detected in the medium. (C) 2003 Elsevier Science Inc. All rights reserved.