This paper deals with the problem of looking for resource allocation mechanisms which would be accepted as just in Sen's capabilities framework. We start by suggesting a way of simplifying Sen's idea of capability by using acapability index which measures the ability of a person to function. Then we look for mechanisms providing allocations which could be deemedjust, in pure distribution problems. An allocation will be called just when its corresponding capabilities are leximin suprema. We provide a characterization result of this mechanism in a framework which mimics Roemer's bargaining in economic environments, in which the role of utility functions is now played by capability indices. When a positive relationship between capability indices and utilities exist, just allocations are optimal in utility terms.