SummaryGiven a random sample of size n from a density f0 on the real line satisfying certain regularity conditions, we propose a nonparametric estimator for rThe estimate is the minimizer of a quadratic functional of the form ~J(r
[r162where ~>0 is a smoothing parameter, J(.) is a roughness penalty, and F, is the empirical c.d.f. of the sample. A characterization of the estimate (useful for computational purposes) is given which is related to spline functions. A more complete study of the case J(r f [d~r is given, since it has the desirable property of giving the maximum likelihood normal estimate in the infinite smoothness limit (~--~c~). Asymptotics under somewhat restrictive assumptions (periodicity) indicate that the estimator is asymptotically consistent and achieves the optimal rate of convergence. This type of estimator looks promising because the minimization problem is simple in comparison with the analogous penalized likelihood estimators.