In patients after gastric surgery it is often difficult to discern symptoms from dumping from other postcibal complaints. Strict criteria for dumping provocation test have not been defined. The sensitivity and specificity of a dumping provocation using 50 g of glucose orally was assessed in 48 patients after gastric surgery, of whom 19 had a typical history of early dumping and 11 had a history of late dumping. Factors were heart rate, packed cell volume, breath hydrogen excretion, and blood glucose concentration. An increase in heart rate of > or = 10 beats/min in the 1st h had a sensitivity of 100% and a specificity of 94% in detecting early dumping. An early rise in breath H2 excretion showed a sensitivity of 84% and specificity of 94%. The nadir blood glucose concentration was not a sensitive or specific indicator for late dumping. Both an increase in heart rate of > or = 10 beats/min and a positive breath hydrogen excretion are sensitive indicators for early dumping. Late dumping is better recognized by the occurrence of subjective symptoms during provocation.