The experiments have been conducted at the Experimental Station of the Cambodian Rubber Research Institute (CRRI) in Kampong Cham province to evaluate the response of three Hevea clones (GT 1, RRIM 712 and IRCA 230) to different concentrations and frequencies of stimulation under S/2 d4 tapping system. The results over a period of seven years showed that the high yield was obtained in S/2 d4 ET 2.5% Pa(1) 12/y in clones RRIM 712, IRCA 230 and GT 1. The yields were increased without increasing the incidence of TPD in the clones tested. The four rounds of stimulation with 3.3% Ethephon was not sufficient, which would be increased to six rounds.