The reference values for triglyceride concentrations in total serum and in its VLDL, LDL and HDL fractions have been produced based on the data obtained in the Mini-Finland Health Survey. The lipoprotein fractions were separated with ultracentrifugation. Efforts were made to obtain reference values for the healthy ambulatory population. Two health-derived selection criteria were used for inclusion of persons into the reference population: those based on the literature available and those based on the recommendations published by the Committee on Reference Values of the Scandinavian Society for Clinical Chemistry and Clinical Physiology, with minor modifications. The frequency distributions of triglycerides especially in total serum and in VLDL fraction were very skewed. Because of that the data were transformed before the calculation of the reference ranges according to the method of Box and Cox [1]. This transformation method appeared to be the best one of many tested methods in obtaining the distributions closer to the normal ones. The 95% inner reference intervals of total serum triglycerides in all subjects and in the two selection groups were 0.5-4.0, 0.5-2.8, and 0.5-3.2 mmol l-1 for men and 0.5-3.4, 0.5-2.3, and 0.5-2.4 mmol l-1 for women, respectively. The age dependence of triglyceride level was prominent in women after the early middle age. The distribution and age dependence of VLDL triglycerides resembled those of total triglycerides. In LDL and HDL fractions the skewness was not as clear as in the whole serum or in VLDL fraction.(ABSTRACT TRUNCATED AT 250 WORDS)