This study on the early diagnosis of forest decline in Norway spruce (PLcea abies), using measurements of the physical, chemical and biochemical properties of foliage, was a continuation of the pilot forest survey undertaken in 1986. The results from that survey, and subsequent measurements and statistical analyses, suggested potential diagnostic tests for evaluation under controlled experimental conditions. The objective was to investigate the responses of trees to controlled pollutant stresses in terms of the potential diagnostic measurements identified from the field survey. Samples of foliage were taken from a wide range of laboratory and field experiments, and we are very grateful for the collaboration and assistance offered by colleagues who made this material available to us. Biochemical measurements were made at the University of Lancaster, histological examination was done at the University of Tlibingen, and leaf surface proper tfes were measured at the Institute of Terrestrial Ecology. This report presents the results from measurements made during 1991 on trees from the open-air field fumigation experiment conducted by National Power and Power Gen (formerly Central Electricity Generating Board) at Liphook. in S. England, and reviews the interim annual reports from this study t o provide overall conclusions and recommendatians.