Sugars and organic acids are important determinants of taste in fruits and vegetables. Based on the enzymatic analyses originally developed by Boehringer-Mannheim, rapid and reliable microplate-based assays were devised for glucose, fructose and sucrose in tomato and orange juice, and citrate and L-malate in tomato. These microplate assays were used to compare some commercially available tomato types, and to study the compartmentation of sugars and acids between pericarp and locular tissue of tomato fruit. The microplate format allows analysis of many samples per day and the only apparatus required is a microplate reader.