This manual, one of a series prepared for the guidance of research workers conducting studies as part of the International Biological Programme, contains recommended methods for the analysis of fresh water. The techniques are grouped in the following major sections: Sample Taking and Storage; Conductivity, pH, Oxidation-Reduction Potential, Alkalinity, Total CO2, Acidity; Major Elements (calcium, magnesium, sodium, iron II and III, chloride, sulphate, sulphide, carbonate and bicarbonate ions); Minor Elements (nitrogen, phosphorous, and silicon compounds); Trace Elements (boron, cobalt, copper, iron, manganese, molybdenum, vanadium, and zinc); Organic Substances, including biological and chemical oxygen demand; and Dissolved Gases (oxygen, nitrogen, carbon dioxide, hydrogen, and methane). There is a theoretical addendum considering the electrochemical properties of water, a bibliography of handbooks and other references, a list of equipment manufacturers, and an appendix containing a preliminary report on the effect of brackish waters on the recommended chemical techniques. (AL)