Clinical strains of Stenotrophomonas (Xanthomonas) maltophilia often show large, growth temperature-dependent, variations in their susceptibility (TDVS) to aminoglycoside antibiotics. Strains showing more than a fourfold increase in susceptibility between 30 degrees and 37 degrees C (TDVS+ strains; n = 23) were contrasted with those showing lesser variation (TDVS- strains; n = 15) in studies of growth temperature-dependent variation in protein and cell-wall lipopolysaccharide (LPS) electrophoresis patterns in an attempt to determine the mechanism of TDVS. Several proteins showed increased intensity with increasing growth temperature. These comprised bands at c. 65, 55, 42.5, 26 and 21.5 kDa in the whole cell proteins, an outer membrane protein band at c. 21.5 kDa, and cytoplasmic membrane protein bands at c. 42.5 and 27 kDa. Two whole cell protein bands at c. 30 and 24 kDa and three outer membrane protein bands at c. 45, 30 and 24 kDa decreased in intensity with increasing growth temperature. However, there was no correlation with the extent of variation in susceptibility, either in the extent of temperature dependent changes in protein banding patterns, or the presence or absence of specific protein bands. By contrast, temperature-dependent variation in LPS patterns correlated well with TDVS. TDVS+ strains yielded intense ladder patterns of more than 30 discrete bands, and the mean molecular weight of the ladder pattern was markedly higher at growth temperatures < or = 30 degrees C, than at > or = 37 degrees C. TDVS- strains gave a clearly distinct high mol. wt LPS banding pattern showing fewer, less intense bands and a smaller and less consistent shift in mean molecular weight with temperature. Strains which were clearly resistant at 30 degrees and 37 degrees C, had a high mol. wt. polysaccharide component but an absence of the typical LPS-ladder pattern. We conclude that the temperature-dependent variation in the aminoglycoside susceptibility of this species was not correlated with any detectable change in protein composition, but correlated well with changes in LPS structure.