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In vitro-grown shoots of `Doyenne d'Hiver' pear (Pyrus communis L.) were maintained for 7 days on 16-h photoperiods at photosynthetic photon fluxes (PPF) of 90, 180 or 270 μmol·m-2·s-1 and irradiated 6 h per day midway through the photoperiod at 0.2 (-UV-B) or 12.0 (+UV-B) kJ·m-2·d-1 of biologically effective ultraviolet-B (UV-BBE) radiation. Increased ethylene production from UV-BBE-treated shoots as compared to the control was recorded after 24 h in cultures grown under 90 and 180 μmol·m-2·s-1 and after 72 h in shoots grown under 270 μmol·m-2·s-1; PPF level had little effect on amount of ethylene evolved. Proliferation was highest at 270 μmol·m-2·s-1, but UV-BBE decreased proliferation and increased apical necrosis. UV-BBE treatment increased lipid peroxidation after 24 h based on malondialdehyde (MDA) determination, but thereafter had no consistent effect on MDA. UV-BBE exposure slightly decreased the monogalactosyldiacylglycerol/digalactosyldiacylglycerol ratio during the initial 24 h, showing an effect on chloroplast membranes.