We have developed a simple technique for the investigation of cellular metabolism and growth in cultured human fibroblasts which facilitates experiments using up to 3 x 10(5) cells in each of 100 or more culture vessels. The method has been used to study cell growth, glucose utilization and oxidation, and protein, RNA and DNA sysnthesis. The use of radiolabeled substrates in tracer experiments is simplified since transfer of cell material is not required. Methods for measuring both total cellular protein and DNA have been adapted to this culture system. Although we have used this tecnique for fibroblast cultures, it also can be easily applied to experiments on any other type of cell that can be grown in a monolayer.