OBJECTIVES: Glomerular filtration rate (GFR) is widely accepted as the best overall measure of kidney function. Cystatin C is a novel endogenous GFR marker that has been shown to be superior to creatinine for estimation of GFR in several studies. There is a need for cystatin C assays adapted to routine chemistry instrument to minimize turnaround times and allowing 24 h/day availability. MATERIALS AND METHODS: We have evaluated a new cystatin C assay developed for Architect cSystem (Abbott Laboratories, Abbott Park, IL, USA). RESULTS: The cystatin C assay showed good agreement with the corresponding assay from Dade Behring (Deerfield, IL, USA). The assay has a very low total imprecision and a good linearity. CONCLUSIONS: The new cystatin C assay is an interesting alternative to current cystatin C assays. On an Architect cSystem the assay can be performed with the same turnaround times and availability as creatinine.