In this article we consider sums S(t) = Sigma(n)psi(tf(n/t)), where psi den
otes, essentially, the fractional part minus 1/2, f is a C-4-function with
f " non-vanishing, and summation is extended over an interval of order t. F
or the mean-square of S(t), an asymptotic formula is established. If f is a
lgebraic this can be sharpened by the indication of an error term.