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Variability in the emission rates of isoprene and monoterpenes from individual leaves of Eucalyptus globulus was investigated with a laboratory gas exchange system and an environmental control leaf cuvette. For individual leaves, with constant environmental conditions, short‐term (1 hour) fluctuations in isoprene emission rates were less than 3% while day‐to‐day fluctuations averaged 14%. Leaf‐to‐leaf variations were much larger (62%). Fluctuations with time and leaf‐to‐leaf variability in CO₂ assimilation rates were of the same order as isoprene, while monoterpene variations were higher. Leaf age was identified as one of the factors contributing to leaf‐to‐leaf variability in CO₂ assimilation and isoprene and monoterpene emission rates. Monoterpene emission rates were not influenced by light intensity or CO₂ mixing ratio. The observed temperature dependence was the same for α‐pinene and 1,8‐cineole (an …