The additive gas effect on the discharge time lag of the address pulse was investigated in an ac plasma-display panel (PDP) with a Ne + 13% Xe gas mixture. A small amount of Kr, N-2, and Ar gas, respectively, was added to a Ne + 13% Xe gas mixture to improve the address discharge time lag of an ac PDP. It was found that the address discharge time lag was improved by adding a small amount of Kr gas (up to 2%) to the Ne + 13% Xe gas mixture and thereafter worsened. In the case of the addition of Ar gas to Ne + 13% Xe, the discharge time lag of the address pulse was not improved. The concentration of N-2 in the Ne + 13% Xe gas mixture was varied from 0.013% to 0.187%, and its effects on the address discharge time lag were investigated. The time lag for the address discharge with a Ne + 13% Xe + 0.013% N-2 gas mixture was improved.