Four methods for assessing sensitivity to the bitterness of phenylthiocarbamide (PTC) and propylthiouracil (PROP) were compared. Good agreement was found among results from forcedchoice detection thresholds, recognition thresholds, and category ratings of single stimuli. Testing by means of papers impregnated with these compounds led to a high incidence of false positive responses from insensitive subjects. Phenylthiocarbamide was a slightly better discriminator of sensitive from insensitive subjects than was propythiouracil. Category ratings of the intensity of the antimodal PTC threshold concentration are a valid, reliable and efficient screening method. Relative safety in the use of PTC and PROP is discussed.