A screen of a GPCR against Pharmacopeia's combinatorial libraries was performed using 1,536-well plates in a 1.5-microl assay volume with an LSI that was specially modified to enable detection at these volumes. The screen encompassed approximately 4 x 10(6) compounds. The assay uses a CHO cell line that expresses human CXCR1. The plate format chosen was the Corning 1536 low-profile wafer plate. The performance of the screen is evaluated, and the necessity to obtain cytotoxicity data from the same well is described.