This paper deals with kernel non-parametric estimation. The multiple kernel
method, as proposed by Berlinet (1993), consists in choosing both the smoo
thing parameter and the order of the kernel function. In this paper we foll
ow this general idea, and the selection is carried out by a combination of
plug-in and cross-validation techniques. In a first attempt we give an asym
ptotic optimality theorem which is stated in a general unifying setting tha
t includes many curve estimation problems. Then, as an illustration, it wil
l be seen how this behaves in both special cases of kernel density and kern
el regression estimation.