An automated method for the determination of ceruloplasmin activity was developed and validated in canine serum. The method is based on the in vitro oxidase activity that this protein shows with substances such as p-phenylenediamine. In order to determine optimum assay conditions, the effects of the substrate concentration, buffer pH, reaction time and EDTA on the reaction were evaluated. The precision of the assay was good with within-run and between-run coefficients of variation lower than 10%. The method measured the ceruloplasmin values in a proportional and linear manner (r = 0.99) with a limit of detection of 0.0007 +/- 0.0001 Delta Abs/min. A temperature of -20 degrees C kept the reagent stable for 30 days. The method is cheap and easy to adapt to any automated biochemical analyser, considerably decreasing the processing time required with the manual method. Additionally it allows to differentiate dogs with pyometra and trauma from clinically healthy dogs.