The emphasis being placed on the need for assessments to determine the impacts of acidic rain has resulted in the initiation of many dose-response studies. Experimental design parameters and model evaluation play important roles in the overall conclusions of such studies. To illustrate the importance of some of these factors, three dose-response studies on radish (Raphanus sativas L.) plants exposed to simulated rain were performed in a greenhouse. Significant negative effects on marketable yield occurred from simulated rain having pH levels below 3.8 in one experiment and below 3.4 in another. The apparent threshold level may have been dependent on environmental conditions which affected overall growth rates. (Copyright (c) 1985 Pergamon Press Ltd.)