Polyphasic chlorophyll α fluorescence represents a promising tool for detection of plant tolerance to various environmental stresses. In pot vegetation experiments, plants of seven winter wheat varieties were screened for their drought tolerance. The drought stress was initiated in plants by withholding water at the beginning of anthesis. While water content was measured continuously as relative water content (RWC), fast chlorophyll α fluorescence kinetics was measured and analysed on dehydrating intact leaves by the JIP-test (analysis of O-J-I-P fluorescence transient). Maximum quantum efficiency of PS II photochemistry (F_V/F_M) parameter was almost unaffected by dehydration until the severe water stress occurred. In contrast to this a continuous decrease of performance index (PI_abs) parameter (Strasser et al. 1995) was observed from the very beginning of dehydration following the decrease of RWC. Statistically significant differences were also found in the PI_abs parameter among all tested varieties. The results show that PI_abs may serve as an index of plant/variety vitality and/or sensitivity to water stress reflecting their different drought tolerance.