The aim of the study was to examine sequential changes in serum levels of the aminoterminal propeptide of type III procollagen (S-PIIINP) after acute myocardial infarction (AMI), and to assess the value of S-PIIINP as a predictor of outcome. The study group comprised 74 patients with AMI, and 24 patients in whom AMI was suspected but disproved. S-PIIINP changed characteristically after AMI, and in patients not receiving thrombolytic therapy or having cardiogenic shock, the changes correlated to peak enzyme values (r = 0.4, p < or = 0.03). S-PIIINP was higher at days 0 to 2 in nonsurviving AMI patients than in survivors (p < 0.05). With use of either the upper quartile for S-PIIINP at day 0 for nonsurviving AMI patients or the mean value of S-PIIINP in a normal population plus 2 SDs as a cutoff, the predictive value of a negative test ranged from 0.79 to 0.87 at days 0 to 2, and the predictive value of a positive test ranged from 0.39 to 0.67. Thus, S-PIIINP on admission and for the following few days after AMI is higher in patients with poor outcome.