Measurements were made of the rates of respiration of self-incompatible stigmas of Oenothera which had been heat treated for 5 minutes at 45 °C and 50 °C, and of self-compatible stigmas at 50 °C. Fifty-degree treatment, which causes partial inactivation of self-incompatibility, lowered the respiration rate to about one-half that of the untreated controls. Forty-five-degree treatment, which does not affect self-incompatibility, had little effect on the respiration rate. Heat treatment had less effect on the respiration rates of self-compatible Oenotheras. The correlation between the effect of heat treatment of lowering respiration rate and overcoming self-incompatibility indicates that normal metabolic level may be necessary for self-incompatibility.