  We present an analysis of interstellar Na I (lambda=3302.37\AA, 3302.98\AA),
Ti II (lambda=3383.76\AA) and Ca II K (lambda=3933.66\AA) absorption features
for 74 sightlines towards O- and B-type stars in the Galactic disc. The data
were obtained from the UVES Paranal Observatory Project, at a spectral
resolution of 3.75km/s and with mean signal to noise ratios per pixel of 260,
300 and 430 for the Na I, Ti II and Ca II observations, respectively.
Interstellar features were detected in all but one of the Ti II sightlines and
all of the Ca II sightlines. The dependence of the column density of these
three species with distance, height relative to the Galactic plane, H I column
density, reddening and depletion relative to the solar abundance has been
investigated. We also examine the accuracy of using the Na I column density as
an indicator of that for H I. In general we find similar strong correlations
for both Ti and Ca, and weaker correlations for Na. Our results confirm the
general belief that Ti and Ca occur in the same regions of the interstellar
medium and also that the Ti II/Ca II ratio is constant over all parameters. We
hence conclude that the absorption properties of Ti and Ca are essentially
constant under the general interstellar medium conditions of the Galactic disc.
