Previous evolutionary computations of horizontal branch stars have bee
n extended to the range of ''thin-envelope'', very hot stellar models,
in order to make available a homogeneous set of models covering the w
hole range of theoretical horizontal branch temperatures. We present e
volutionary tracks for selected models of various metallicities, inten
ded to represent the theoretical counterpart of hot stars populating e
xtremely blue horizontal branches as well as to provide an input for d
etailed population synthesis programs devoted to study the origin of t
he ultraviolet light in old stellar systems. The role of metallicity i
n governing the evolutionary approach to the asymptotic giant branch a
nd the contribution of the models to the UV flux are both shortly disc
ussed.