A new estimator is proposed for the parameter C=4Nc,
where N is the population size and c is
the recombination rate in a finite population model without selection.
The estimator is an
improved version of Hudson's (1987) estimator, which takes advantage
of some recent theoretical
developments. The improvement is slight, but the smaller bias and standard
error of the new
estimator support its use. The variance of the average number of pairwise
differences is also
derived, and is important in the formulation of the new estimator.