Photosynthesis, respiration and chlorophyll fluorescence parameters were determined in peach (Prunus persica L. cv. Dixired) leaves naturally infected by Taphrina deformans (Berk.) Tul. and in healthy leaves (controls), in two successive springs. A drastic decrease in net photosynthesis and an evident increase in respiration in curled leaves were noted. The instantaneous PSII fluorescence yield, with no (F0) and with (F0) quenching component, and steady state fluorescence yield (under actinic light, Fs) were essentially unchanged. Maximal fluorescence in dark-adapted (Fm) and illuminated (F′m) leaves and the corresponding variable fluorescence (Fv and Fv) clearly decreased. The indicators of PSII quantum yield (Fv/Fm) in dark-adapted leaves, and the potential PSII excitation capture efficiency (F′v/F′m) and the quantum yield of PSII (qp [F′v/F′m]) in the light were also significantly lower in curled leaves. Decreasing tendencies were also noted for the PSII photochemical yield (photochemical quenching, qp) and in the energy status of the chloroplast (non-photochemical quenching, qN, and Stern-Vollmer value, NPQ) although the differences were not always significant. In curled leaves the main alteration documented is the imbalance between the drastic inhibition of CO2 fixation and the moderate decrease in photochemical reactions (i.e. Fv/Fm and ΔF/F′m), indicating changes in the energy flux.