Abstract
It is shown that, with certain assumptions, the author's model of a degenerate gas of spin bipolarons can account for a value of the Hall constant R H proportional to 1/T, as observed for YBCO. We discuss also the behaviour of La2-xSrxCuO4, and other high-temperature superconductors, and suggest that the differences between their behaviour and that of YBCO are related to disorder.