This article presents a detailed interpretation and discussion of the deuterium and tritium measurements carried out on six hailstones. The isotopic variations of condensed water in a hail cloud are studied on the basis of a cloud model proposed by A. J. Chisholm. The influence of the existence of a liquid water accumulation zone and of the presence of hailstones on isotopic profiles is also analyzed. The importance of tritium analysis is demonstrated, and conditions of validity of the isotopic model proposed by L. Merlivat, G. Nief, and E. Roth in the case of deuterium are defined. The interpretation and discussion of the experimental results are based mainly on the measurements made on three hailstones produced during a storm on August 7, 1971, in the province of Alberta in Canada. It is demonstrated that the hailstones were formed during a succession of upward and downward movements, at least two of the latter occurring in the updraft core, and that the distribution of the updraft velocity with altitude was not stable during the storm, a finding which is in agreement with its multicellular nature.