The relationship of train-of-four (TOF) ratio to the depression of the first twitch (TD) was investigated in 16 patients given pancuronium in doses insufficient to eliminate the fourth response in the train. In ten patients the block was allowed to spontaneously recover (Group 1) and in six it was reversed with neostigmine (Group 2) once maximum depression of TOF ratio had occurred. Maximum depression of the first response occurred in 6.5 ± 4.3 min (mean ± SD). Maximum depression of the TOF ratio was not present until 28.0 ± 11.0 min. TOF ratio was usually still decreasing when recovery of TD had begun. However, once the TOF ratio began to recover, the recovery rates for TD and TOF ratio were similar in both the spontaneously recovering and the reversed groups. TOF ratio at complete TD recovery was 74.9 ± 15.7 and 86.2 ± 15.4% for the two groups. A kinetic analysis yielded significantly different elimination rate constants for the two effects from the “effect compartment.” These findings suggest that these two effects of pancuronium are exerted at different sites.