Radish plants were exposed three times per week to simulated acidic rain at pH values of 2.6 to 5.4 over the course of four weeks in trials performed at Argonne, IL: Ithaca & Upton, NY; Corvallis, OR; Oak Ridge, TN; and Toronto, Canada. Uniform genotype, soil media and planting techniques, treatment procedures, biological measurements, and experimental design were employed. Growth of plants differed among trials as a result of variation in greenhouse environmental conditions according to location and facilities. Larger plants underwent greater absolute but lower relative reduction in biomass after exposure to the high levels of acidity. A generalized Mitscherlich function was used to model the effects of acidity of simulated rain or dry mass of hypocotyls using data from three laboratories that performed only one trial each, were used to test the model. When the laboratory by trial effect was removed (influence of different growth conditions), lack of fit to the Mitscherlich function was insignificant. Thus, a single mathematical model satisfactorily characterized the relationship between acidity and mean plant response. The pH value associated with a 10 percent reduction in mass was 3.3 + or - 0.3 for hypocotyls. No value was estimated for shoots because effects on shoots were not significant. (Copyright (c) 1988 APCA.)