Myotonic dystrophy (DM) is considered an inherited membrane disorder, but the basic defect is unknown. We studied plasma catecholamines as well as lymphocyte and muscle beta-adrenergic receptor densities and functioning in 19 DM patients and 15 control subjects. Plasma adrenaline and noradrenaline concentrations were not significantly different between DM patients and controls. In isolated lymphocytes basal cAMP production was 157 +/- 26 pmol/mg protein/10 min in DM patients and 91 +/- 12 pmol/mg protein/10 min in controls (n.s.), whereas isoproterenol-stimulated cAMP production was significantly higher in DM patients (285 +/- 42 pmol/mg protein) compared with control subjects (168 +/- 21 pmol/mg protein, P less than 0.05). Lymphocyte beta-adrenoceptor densities were similar among DM patients (50 +/- 3 fmol/mg protein) and controls (47 +/- 5 fmol/mg protein). beta-Adrenoceptor densities were also similar in muscle biopsy specimens (12.9 +/- 1 in DM and 13.1 +/- fmol/mg protein in controls). The correlation between lymphocyte and skeletal muscle receptor densities was r = 0.35 in DM patients and r = 0.22 in controls. The results do not support the hypothesis of adrenergic dysfunction in DM despite its membrane involvement.