A calorimetric study has been made on the dissociation processes in water of the free alpha-amino group of the amino terminal residue and the free alpha-carboxyl groups of the carboxyl terminal residue in a series of dipeptides having valine as first common term. These values have been compared with those of the roton dissociation processes related to the same groups of the corresponding single alpha-amino acids. The results of this series have also been considered in relation to those from another series of dipeptides, previously studied, in an effort to compare the effects of different chains on the dissociation processes of the free alpha-carboxyl and free alpha-amino groups.