Seventeen severely ill patients with acute myocardial infarction (AMI) (12 men and 5 women; mean age 65) and 37 healthy persons with similar age and sex distribution were investigated. Regional left ventricular wall motion was studied in terms of mean wall velocity, in 16 segments, 8 basal and 8 apical, by M-mode echocardiographic (Echo) mapping from 6 probe positions. Adequate Echo registrations were obtained from 88% of the total of 864 segments. The best classification (88.5%) of normal and infarcted segments was obtained with a -30% deviation of mean systolic wall velocity (Vmean) values from the mean values of the control segments (CS). Non-infarcted segments (NIS) in the AMI group had significantly lower Vmean values than the CS (p less than 0.001). Subendocardially (SIS) and transmurally (TIS) infarcted segments could be clearly separated from both CS and NIS (p less than 0.001). Per cent deviation of Vmean from the mean value of the control segments (PD-V) for SIS varied considerably overlapping CS, NIS and TIS. With a PD-V between 0 and -30% the probability of NIS is 94%, SIS 6% and TIS less than 1%. A PD-V more than -66% was rarely seen among NIS (2%) but was the normal finding in TIS (94%).