Magnetic resonance imaging was performed in 8 patients with muscle disease and 6 normal controls. High intensity areas of varying dimensions were found in thigh muscles of the patients with progressive muscular dystrophy (PMD) and congenital myopathy. Shortened T, and prolonged T2 values with disease progression were characteristic. The T, values were variable and prolonged, T2 values were more characteristic of progressive muscular degeneration. The T, value may help to detect the early stage of PMD. Magnetic resonance imaging is useful in detecting the muscle lesions in PMD and essential for selection of a biopsy site. © 1989.