Parameters of fibrinolysis, including euglobulin fibrinolytic activity, tissue-type plasminogen activator (t-PA) antigen, plasminogen activator inhibitor (PA-inhibitor) activity, and plasmin-alpha 2-antiplasmin complex (PAP) were studied in 62 patients (35 women and 27 men; ages 53 +/- 16 years) with either insulin-dependent (IDDM) or noninsulin-dependent (NIDDM) diabetes mellitus. Compared to a control group of similar age (n = 57), the diabetic patients had a significantly lower mean euglobulin fibrinolytic activity (1.2 +/- 0.7 vs. 1.7 +/- 1.1 ng/ml, p less than 0.01) but significantly higher mean t-PA antigen (15.7 +/- 8.4 vs. 6.6 +/- 2.9 ng/ml, p less than 0.001) and PA-inhibitor activity (2.6 +/- 1.3 vs. 1.5 +/- 0.7 IU/ml, p less than 0.001) levels. Significant univariate correlations were observed between PA-inhibitor activity and age (r = 0.32, p less than 0.05), diastolic blood pressure (r = 0.42, p less than 0.01) and euglobulin fibrinolytic activity (r = -0.40, p less than 0.01). In multivariate analysis, only body mass index (positively) and euglobulin fibrinolytic activity (negatively) remained significantly related to PA-inhibitor activity in the total diabetic population as well as in the NIDDM group. The only parameter in the IDDM group significantly related to PA-inhibitor activity was diastolic blood pressure. These results suggest that PA-inhibitor plays a role in the regulation of fibrinolysis in diabetes patients and that factors like obesity and hypertension may be related to reduced fibrinolysis via PA-inhibitor levels.