Epidermal windows on leaves may increase the surface area available for light absorption by allowing the transmission of light through the internal succulent, water-storage hydrenchyma and illuminating the chlorenchyma tissue from the inside of the leaf. This would appear to be advantageous by increasing photosynthetic rates in these CAM plants, especially for taxa that grow partially underground in their native habitats. This hypothetical benefit of windows, however, has rarely been experimentally investigated. Thus, net CO2 exchange was measured on plants of Haworthia truncata, Lithops olivacea (both with a below-ground growth habit), and Peperomia graveolens (with an aboveground growth habit) with their windows covered by reflective tape, and the results were compared with plants having unobstructed windows. Despite past assumptions about the function of leaf windows in these succulents, net C02 exchange and nocturnal accumulations of malic acid were not significantly greater in plants with unobstructed windows. Key words: Crassulacean acid metabolism, Haworthia truncata, Lithops olivacea, Peperomia graveolens, windows.