In the present study we used patient data to calculate laboratory-specific indirect reference intervals. These values were compared with reference intervals obtained for a healthy group according to recommendations of the International Federation of Clinical Chemistry and Laboratory Medicine and manufacturer suggestions. Laboratory results ( 422,919 records) from all subjects of 18-45 years of age over a 1-year period were retrieved from our laboratory information system and indirect reference intervals for 40 common analytes were estimated using a modified Bhattacharya procedure. Indirect reference intervals for most of the biochemical analytes were comparable, with small differences in lower [alkaline phosphatase (ALP) ( male), alanine aminotransferase ( ALT), creatine kinase, iron ( male), total iron-binding capacity, folic acid, calcium ( female), lactate dehydrogenase (LDH), lipoprotein ( a) [Lp(a)], thyroid-stimulating hormone (TSH), total triiodothyronine ( T-3), direct bilirubin, apolipoprotein A-I ( apoA-I), glucose, homocysteine, total cholesterol, ferritin, total protein, ceruloplasmin, sodium, blood urea nitrogen (BUN) and uric acid ( female)] and/or upper limits [albumin, ALP ( male), amylase, apoA-I, creatine kinase-MB (CK-MB), total iron-binding capacity, phosphorus, glucose, total cholesterol, g-glutamyltransferase (g-GT), magnesium, total protein, high-density lipoprotein cholesterol (HDL-C), total T-3, ALP ( male), ALT, aspartate aminotransferase (AST) ( male), direct bilirubin ( male), creatine kinase, iron, folic acid ( female), Lp( a), uric acid and triglycerides], to the reference intervals determined for healthy subjects in our laboratory. The indirect reference intervals, with the exception of a few parameters ( creatinine, direct total bilirubin, calcium, BUN and potassium), were not similar to the reference intervals suggested by the manufacturers. We conclude that laboratory-specific reference intervals can be determined from stored data with a relatively easy and inexpensive method. Indirect reference intervals derived from stored data may be particularly suitable for the evaluation of results for the presenting population.