Microfungi on decomposing alder leaves were isolated monthly by the soil-wash technique from October until the leaves disappeared in June. The isolates were tested for their ability to grow on gelatine, starch, pectin, cellulose, chitin, and gallic acid at 10°C. A large proportion of the isolates from the green leaves was able to use gallic acid. The highest potential activity on the carbohydrates was found in the cold period, with a cellulolytic maximum in February caused by a Phoma sp. A high chitin-utilization value, mainly from the activity of different Mortierella spp, was attained in March, indicating decomposition of the hyphal walls of previously-active fungi. Cladosporium herbarum and C. cladosporioides were the most frequent fungi with a versatile activity pattern.