The thigh regions of 10 patients suffering from polymyositis were examined by magnetic resonance imaging (MRI) at 1.5 T; follow-up examinations were performed in all patients. MRI findings were correlated with findings at physical examination and serological parameters. In four patients focal areas of hyperintensity on T2-weighted (T2W) spin echo (SE) images were found within muscles. They were not detectable on T1-weighted (T1W) images. In three of these cases enhancement within the musculature was seen following i.v. administration of Gd-DTPA on T1W images. In another five patients there was varied replacement of muscle by fatty tissue. In one patient the muscle appeared completely normal. On follow-up three patients showed definite changes in imaging findings; two correlated well with clinical and biochemical findings while the third exhibited massive deterioration clinically with mild improvement on imaging. Seven patients exhibited no change on MRI; four of these had shown a significant clinical change in the course of the disease, whilst three were clinically stable. In our small series MRI using SE technique (T1W and T2W) and contrast enhancement to date seems to be of limited value for the assessment of muscular changes during therapy. The i.v. use of Gd-DTPA did not add to MRI's diagnostic value in this series.