We consider Gauss quadrature formulae Qn, ne N, approximating the integral 1(f)--/_\ w(x)f(x)dx, w = W/p,,i = 1,2, with W(x) = (1 -x)a(l + x)ß,a,ß = +1/2 and Pi(jc) = 1 + a2 + 2ax, p2(x) = (2b + l)x2 + b2, b > 0. In certain spaces of analytic functions the error functional R" '.-I -Q" is continuous. In [1] and [2] estimates for ||Ä"|| are given for a wide class of weight functions. Here, for a restricted class of weight functions, we calculate the norm of Rn explicitly. K = 0