Tripler metastable species produced by intersystem crossing from the (A) over tilde((1)A(u)) state of acetylene has been detected by the sensitized phosphorescence method. A sensitized phosphorescence signal was observed from vibronic levels lying lower than the potential energy barrier for dissociation in the a state suggested previously, but was not observed from levels higher than this barrier. The lifetimes of tripler states produced by intersystem crossing from the (VK1)-K-3(J’ = 2) and (VK1)-K-4(J’ = 2) levels were estimated to be 100 and 80 mu s.