Quantitative assessments of the incidence and severity of Mycosphaerella leaf disease were made on nine provenances (encompassing the four subspecies) ofEucalyptusglobulusLabill. over three seasons in 1990 in a trial in Victoria, Australia. Defoliation was also assessed and tree height and diameter measured. Mycosphaerella leaf disease increased rapidly from winter to spring with disease incidence reaching 100% in most provenances by summer. There were highly significant differences in disease severity among provenances, with provenances fromE.globulusssp.globulusKirkpatrick andE.globulusssp.bicostata(Maid, et al.) Kirkpatrick being the most severely affected, while provenances fromE.globulusssp.maidenii(F. Muell.) Kirkpatrick andE.globulusssp.pseudoglobulusKirkpatrick were only slightly affected. There were also highly significant differences among provenances withinE.globulusssp.globulusandE.globulusssp.pseudoglobulus. There was a high correlation between disease severity in summer and defoliation, suggesting that Mycosphaerella leaf disease was the main causal agent in leaf fall. There was also a high negative correlation between disease severity and growth rate. This study shows the potential benefits of selecting resistant provenances ofE.globulusto maximise production from plantations in areas where Mycosphaerella leaf disease is a problem.