SummaryActinomycetes of the family Actinoplanaceae, especiallyActinoplanes, are readily isolated from the flowing waters of local rivers and streams and it seems clear that such lotic environments are favoured for colonization by these organisms. In this contribution evidence is produced that part at least of this activity can be ascribed to the utilization of wood as a growth substratum. Some other aquatic Actinomycetes of less certain affinity were also shown to be capable of growth on wood, under the conditions of pure culture.