Abstract: Substantial quantities of calcium oxalate annually reach the ground with the forest litter, primarily in the form of calcium oxalate monohydrate. More calcium oxalate is produced by soil fungi, in the form of both monohydrate and dihydrate. The quantities of calcium bound in calcium oxalate are notably high in litter as compared with the amounts of exchangeable calcium. In the case of humus, on the other hand, the corresponding proportion is usually small because oxalate breaks down rather rapidly in the soil. For some reason, however, it seems that calcium oxalate accumulates to a much greater extent in white rot than in brown rot. Despite the fact that a large number of basidiomycetous fungi are capable of using oxalate, they seem to be of only minor importance in the break-down of calcium oxalate.