ABSTRACTGrowth on different media, substrate utilization patterns, water-soluble protein electrophoretic profiles, as well as pectinase and amylase multilocus enzyme analyses were used to characterize thirty-seven endophytic strains ofLeptostromaisolated from needles ofPicea abies, Abies alba, andA. balsamea.Among substrate utilization tests, only proteolytic activity, almost absent in the spruce isolates but usually present in the others, could be used for characterization of strains. All isolates tested positive for the Bavendamm reaction and were able to utilize soluble starch and cellulose. Electrophoresis of water soluble proteins provided a reliable method to distinguish isolates from different hosts because electromorphs were host-specific. Electrophoresis of pectic enzymes allowed a more accurate differentiation of strains within host, but, on the whole, host-specificity of electromorphs was confirmed. Amylolytic activity was absent inca50% of the strains tested and the same electromorph was shared by roughly 80% of the remaining isolates. The results of this study support the hypothesis that distinct species ofLeptostroma, which are morphologically almost indistinguishable from each other, colonize apparently healthy needles ofA. alba, A. balsamea, andP. abies.Ecophysiologically all isolates showed biochemical attributes associated with needle penetration and long-term residence within needles.