The quantitation of myoglobin (Mb) in serum and urine is of clinical importance for the differentiation of myocardial infarction from degenerative cardiac disorders as well as for the detection of traumatic and atraumatic rhabdomyolysis, followed frequently by acute kidney failure. A simple method is described to prepare myoglobin from human muscle extract by negative pressure ultrafiltration and dialysis. By a combination of electrophoretic procedures, this preparation was analysed for purity. Saline myoglobin solutions after deep freezing loose rapidly their immunoreactive Mb content. By addition of pure albumin, not containing heme binding proteins, a stable Mb solution was obtained. This has been used as standard (5--50 microgram/ml) in radial immunodiffusion sensitive for detecting 0.2--1 microgram Mb/ml.