Soybean, Glycine max L., and elodea, Elodea canadensis Michx, leaves were exposed to sublethal and lethal temperatures and examined by light microscopy. Loss of chlorophyll and swollen chloroplasts were observed in cells of elodea leaves exposed to sublethal temperatures. At the thermal death point of leaf cells of elodea and soybean, there was a disorganization of the tonoplast membrane, plasmalemma, and chloroplast membranes. Approximately 40% of the cells in elodea and 50% of the cells in soybean leaves exhibited oriteria of cell death when exposed to a temperature which induced necrotic leaf tissue. Plasmolysis of leaf cells of elodea and soybean occurred at lethal temperatures, but did not appear to be the primary cause of cellular death. The primary effect of lethal temperatures on the leaf cells used in these experiments is disintegration of the cellular membranes.Following exposure of attached elodea leaves to lethal temperatures, changes in leaf cells were periodically observed with a light microscope. In low temperature treatments, (43 through 52 degrees ), the percentages of cells exhibiting criteria of death 12 days after treatment did not change from the percentages determined immediately after treatment. All treatments above 52 degrees resulted in 40% or more of the cells exhibiting criteria of cell death immediately after treatment. In these treatments, this resulted in all cells exhibiting criteria of death on the fourth day after treatment.