Treatment of HeLa-S3 cells with 640 u/ml of human beta interferon (HuIFN-beta) in suspension culture increases the cell volume and the heterogeneity of the population with respect to cell size, as measured by Coulter electronic volume analysis. Based on such analysis, the cell surface area is increased 11% by 24 h, and 42% by 48 h after beginning of interferon treatment. Binding of [125I] Concanavalin A (measured at 22 degrees C) is increased 75% by 24 h, and 120% by 48 h on a per-cell basis. It follows that interferon treatment for 24 h causes a 58% increase in the abundance of functional Con A receptor sites per unit area of cell surface. The further increase in Con A binding after treatment of cells with interferon for 48 h can be attributed to increased surface area of cells.