This paper discusses the determ-nation of difference thresholds (ED50) by least squares procedures. A table of weights (W) to correct ED50 for chance probability was constructed for paired and triangle designs. The probability (P) of a correct judgment above chance for the paired design is P = 2p*−1, where p* is the actual proportion of correct responses. For the triangle design, P = (3p*−l)/2. In both designs, P was weighted by W = y2/p*q*, where y2 is the squared ordinate of the normal curve based on P, and q* = 1−p*. An example of the use of the table of weights is provided.