Microwave and optical techniques have been used to measure the decay of the neutral metastable and the charged species in a flowing helium afterglow. Impurity gases, oxygen and argon, are introduced into the afterglow, and measurements of the resulting ionization and excitation yield values for the triplet metastable diffusion coefficient and three‐body combination coefficient of 490 cm2sec−1Torr and 0.25 sec−1Torr−2, respectively. In addition, the ambipolar diffusion coefficient of the molecular helium ion was found to be 724 cm2sec−1Torr. The mean helium pressure was in the range of 5 to 35 Torr and the gas nominally at room temperature. Absolute triplet metastable densities early in the afterglow were also measured.