  The results of nonlinear, convective models of RR Lyrae pulsators with metal
content Z=0.0001 to 0.006 are discussed and several predicted relations
connecting pulsational (period and amplitude of pulsation) and evolutionary
parameters (mass, absolute magnitude and color of the pulsator) are derived.
These relations, when linked with the average mass of RR Lyrae stars, as
suggested by horizontal branch evolutionary models, provide a ``pulsational''
route to the determination of the distance modulus, both apparent and
intrinsic, of RR Lyrae rich globular clusters. Based on a preliminary set of
synthetic horizontal branch simulations, we compare the predicted relations
with observed variables in selected globular clusters (M2, M3, M5, M15, M55,
M68, NGC 1851, NGC 3201, NGC 5466, NGC 6362, NGC 6934 and IC 4499). We show
that the distance moduli inferred by the various theoretical relations are
mutually consistent within the errors, provided that the value of the
mixing-length parameter slightly increases from the blue to the red edge of the
pulsation region.
  Moreover, we show that the relative ``pulsational'' distance moduli fit well
previous empirical results and that the parallax of the prototype variable RR
Lyr, as inferred by the predicted Period-Wasenheit relation, is in close
agreement with the HST astrometric measurement.
