To extend the application of starch-gel electrophoresis to the sarcoplasmic proteins of vertebrate smooth muscle, these extracts must be fractionated by acidification at pH 5 and by ammonium sulphate at 45 % saturation in order to remove the structural proteins and some contaminants which impede the resolution. The extracts of six cow muscles – a white skeletal one, a red skeletal one, the cardiac, stomach, uterus, and carotid muscles – have been analyzed by this method. The patterns have been stained for the major glycolytic enzymes. Enolase, creatine kinase, and lactate dehydrogenase (LDH) make discrimination of the smooth and the striated muscles possible. The smooth muscles contain a much lower amount of glycolytic enzymes and a large number of nonglycolytic bands. Their LDH isoenzymic distribution confirms their high aerobicity. Although many bands are common to the three smooth muscles examined, starch-gel electrophoresis is also able to detect protein differences between the smooth vertebrate muscles of the same species.