Coverslip holder CCH-1 and CCH-2 hold an 11 × 22 mm coverslip with cultured cells attached at the proper position in a standard 12.5 mm cuvette for fluorescence measurements. Adequate space is provided at the base of the cuvette for a magnetic stir bar. Model CCH-2 provides tubing for perifusion of cells during experiments. Both models allow the introduction of reagents by a microsyringe aperture, and are suited for use in C&L; Instruments Model CV-1 fluorescence cuvette accessory.