  We performed a compilation of more than 1000 published spectra of HII regions
in spiral galaxies. The oxygen and nitrogen abundances in each HII region were
recomputed in a homogeneous way, using the P-method. The radial distributions
of oxygen and nitrogen abundances were derived. The correlations between oxygen
abundance and macroscopic properties are examined. There is a significant
difference between the L-Z relationship obtained here and that based on the
oxygen abundances determined through the R_23-calibrations. The oxygen
abundance of NGC 5457 recently determined using direct measurements of Te
(Kennicutt, Bresolin & Garnett 2003) agrees with the L-Z relationship derived
here, but is in conflict with the L-Z relationship derived with the R_23-based
oxygen abundances. The obtained L-Z relation for spirals is compared to that
for irregulars. Our sample of galaxies shows evidence that the slope of the
O/H-M_B relationship for spirals is slightly more shallow than that for
irregulars. The effective oxygen yields were estimated for spiral and irregular
galaxies. The effective oxygen yield increases with increasing luminosity from
M_B=-11 to M_B=-18 (or with increasing rotation velocity from Vrot=10 km/s to
Vrot=100 km/s) and then remains approximately constant. Irregular galaxies from
our sample have effective oxygen yields lowered by a factor of 3 at maximum,
i.e. irregular galaxies usually keep at least 1/3 of the oxygen they
manufactured during their evolution.
