An effort has been made to test the reliability and validity of electrical excitation of the tooth pulp as an algesimetric procedure. Reliability studies consisted of pain threshold determinations of 4 consecutive tests at 15-min. intervals on each of 2 filled teeth in 14 subjects on 6 or 8 different days. Statistical treatment of the data, by analysis of variance reveals that there is a significant difference between 2 teeth in the same head, different subjects and different days on the same tooth and subject, but no significant difference occurred on 15-min. trials on any tooth during the same day. When the study was extended on the same subjects to tests running at 15-min. intervals after oral admn. of 1 gr. codeine phosphate, 5 gr. aspirin plus 5 gr. phenacetin, calcium lactate placebo or no medication, the increments from pre-medication thresholds of the 3 drugs were significantly greater than when no capsule was given. However, there was no significant difference between any of the increments obtained by the 2 drugs or the placebo. Correlation between increments of pairs of teeth after medication was significant on all three drugs and the "dry" run. However, the correlation was best, quantitatively, for codeine, next best for aspirin-phenacetin and least for no medication. The results are considered indicative of the need for an instrument which measures the stimulating current directly, not indirectly. They also indicate that aspirin is not analgesic but probably relieves pain by some other mechanism.