[en] Improvements in plasma performance with pellet injection have been achieved in several tokamaks in recent experiments. On the Impurity Study Experiment (ISX-B), an increase in plasma energy by as much as 50%, has been observed following pellet injection. With 1.5-mm pellets, the value for tau/sub E/, the gross energy confinement time determined from β/sub equil/, has peaked at 1.7 times ISX-B scaling for n/sub e/ = 6 x 10¹³ cm^-3 in both well-gettered and ungettered discharges. Following the peak, in the well-gettered shots tau/sub E/ decays to 1.2 times ISX-B scaling within 50 ms after pellet injection. In the ungettered discharges tau/sub E/ follows the Z-mode scaling that is appropriate to the plasma conditions (P/sub B/ = 1.7 MW, I/sub p/ = 180 kA). Thus, pellet injection in ISX-B shows energy confinement better than that for gas puffing in clean discharges and matches the Z-mode improvement obtained in ungettered discharges. Confinement improvement following pellet injection has also been acheived in smaller (a/sub p/ = 20 cm) plasmas with 1.0 mm diameter pellets. Comparisons of pellet shots which do show this improvement against pellet shots which do not show it was present