Atomic temperature factors (B-values) obtained from X-ray refinement experiments provide empirical estimates of protein mobility that have been correlated with both theoretical simulations of protein dynamics and experimental studies of antibody reactivity. The comparison of B-values with protein solution properties requires adjustment of the apparent atomic mobilities to compensate for the effects of the crystal environment. Here we compare crystallographically independent subunits of the dimeric cytochrome c' from the bacterium Rhodospirillum molischianum to examine how lattice effects influence refined B-values. In addition to local effects on protein mobility at crystal contacts, we show that B-value differences up to 12 A between subunits result from lattice disordering effects that approximate to concerted rotations of the molecules about a crystal symmetry axis.