An approach is described for using patient databases of a hospital information system as a source of reference values for cardiac enzymes. Of a total of 2029 emergency admission patients with serial cardiac enzyme data, 538 patients were considered "healthy" (having no damage in myocardium) because their discharge diagnoses suggested neither myocardial damage nor any other condition that could lead to elevated enzyme activities, and because their serially collected cardiac enzyme activities remained stable. Enzyme activities of creatine kinase (EC 2.7.3.2), creatine kinase isoenzyme MB, lactate dehydrogenase (EC 1.1.1.28), and lactate dehydrogenase isoenzyme 1 of these patients at admission to hospital were considered as suitable health related reference values. The upper (97.5%) reference limits of activities, measured at 37 degrees C according to Scandinavian recommendations, were as follows (age dependent limits given at 25 and at 75 years of age, U/l): creatine kinase men 268, 192; creatine kinase women 200 (no age effect); creatine kinase-MB 16, 24; lactate dehydrogenase 497, 603; lactate dehydrogenase isoenzyme 1 103, 140. For comparison, reference values were also produced conventionally from a group of 246 healthy subjects. Observed effects of age on enzyme activities were quite similar to those in the selected patient group. Calculated reference limits for isoenzymes creatine kinase-MB and lactate dehydrogenase isoenzyme 1 were also similar but reference limits for less cardiospecific total enzyme activities, creatine kinase and lactate dehydrogenase, were more variable between these two groups.(ABSTRACT TRUNCATED AT 250 WORDS)