  We have refined the CORS method, introduced in 1980 for the computation of
the cepheid radii, in order to extend its applicability to recent and extensive
sets of observations. The refinement is based on the computation, from
observational data only, of one of the terms of the solving equation,
previously based only on precise calibrations of photometric colours. A limited
number of assumptions, generally accepted in the literature, is used.\par New
radii are computed for about 70 cepheids, and the resulting P-R relation is
discussed.
