Three types of evidence indicate that stomatal cycling occurs in citrus under field conditions. First, dendrograph records collected from 1963 to 1965 on 30-year-old trees revealed daytime oscillations in trunk diameter, with a period of about 1 h. These oscillations occurred during winter and summer months at two southern California locations. Second, leaf conductance measurements were made on 12-year-old citrus in southern California during clear, mild days in March and April, 1975. Oscillations having a period of shorter than 1 h were observed. Third, oscillations in photosynthesis measured with a Shimshi apparatus were observed on 17-year-old citrus in Israel during clear days in November 1975. In controlled greenhouse experiments on 4-year-old citrus in large pots, cycling in leaf conductance, leaf water stress, and trunk diameter were observed, but the patterns differed with root temperatures of 5 and 25 °C. At 5 °C, cycling began early and decreased later in the day, and water stress and trunk diameter changes lagged behind conductance changes. At 25 °C, cycling became more prominent as the day progressed, and no lag was observed.