AbstractLiterature dealing with the use of bryophytes for water quality assessment is briefly reviewed. Reasons for selection of the two bryophyte species,Eurhynchium riparioidesandFontinalis antipyretica, used in transplantation experiments, are discussed.Results are presented showing that the breakdown of the two bryophyte species, exposed at six stations in the river Ebbw Fawr in the winters of 1970 and 1973, reflects improvements in water quality both downstream of the main source of pollution as a result of dilution and precipitation of pollutants, and over a period of 4 years as a result of improved effluent treatments.Modifications of the technique to deal with various types of pollution are discussed.