Müller cells from adult rabbit retina were cultured at normal (37 degrees C) temperature and under heat shock conditions (42-43 degrees C) for either 1.5 hr or 4 hr. The presence of heat shock proteins of three different molecular weights, and of vimentin, was identified by the use of monoclonal antibodies and of GFAP by a suitable polyclonal antibody coupled in each instance with immunofluorescence microscopy or immuno-electron microscopy. Heat shock conditions resulted in the expression of HSP of molecular weights in the ranges 57-61 kD, 68 kD and 90 kD. The high level of expression of GFAP in unshocked Müller cell cultures (80-90% of cells) was reduced after 1.5 hr of heat shock to 20-30% of cells, and after 4 hr to only 5%. Although the expression of vimentin (90% of untreated cells) was only slightly reduced by heat shock (60-80% of cells) the intracellular staining pattern of vimentin was greatly altered by heat shock. Changes in the expression of HSP, GFAP and vimentin can all be regarded as part of the Müller cell response to heat shock conditions.