A new fully automated nephelometric immunoassay for lipoprotein(a) quantification in human serum was evaluated using the Behring Nephelometer Analyzer. The assay exhibited a good linearity in the concentration range of 110-1,770 mg/l; at higher concentrations, samples were automatically diluted by a factor of 4. The method is simple, robust, and shows an excellent stability of the calibration curve over several weeks. Intra-assay and day-to-day coefficients of variation were 2% and 4.5%, respectively. The method correlated well with electroimmunodiffusion (r = 0.977; n = 123; P = 0.0001). Unspecific turbidity as expressed by an elevated blank value occurred in 3% of all freshly measured samples (n = 392). Storage of the samples for 1 week at 4 degrees C had no significant influence on the results. Frozen sera, on the other hand, cannot be assayed by this method. We believe that this assay is well suited for use in clinical routine work.