  The 1<z<2 redshift window hosts the peak of the star formation and metal
production rates. Studies of the metal content of the star forming galaxies at
these epochs are however sparse. We report VLT-ISAAC near-infrared spectroscopy
for a sample of five [OII]-selected, M_B,AB<-21.5, z~1.4 galaxies, by which we
measured Hbeta and [OIII]5007 emission line fluxes from J-band spectra, and
Halpha line fluxes plus upper limits for [NII]6584 fluxes from H-band spectra.
The z~1.4 galaxies are characterized by the high [OIII]/[OII] line ratios, low
extinction and low metallicity that are typical of lower luminosity CADIS
galaxies at 0.4<z<0.7, and of more luminous Lyman Break Galaxies at z~3, but
not seen in CFRS galaxies at 0.4<z<0.9. This type of spectrum (e.g., high
[OIII]/[OII]) is seen in progressively more luminous galaxies as the redshift
increases. These spectra are caused by a combination of high ionisation
parameter q and lower [O/H]. Pegase2 chemical evolution models are used to
relate the observed metallicities and luminosities of z~1.4 galaxies to galaxy
samples at lower and higher redshift. Not surpringsingly, we see a relationship
between redshift and inferred chemical age. We suppose that the metal-enriched
reservoirs of star forming gas that we are probing at intermediate redshifts
are being mostly consumed to build up both the disk and the bulge components of
spiral galaxies. Finally, our analysis of the metallicity-luminosity relation
at 0<z<1.5 suggests that the period of rapid chemical evolution may take place
progressively in lower mass systems as the universe ages. These results are
consistent with a ``downsizing'' type picture in the sense that particular
signatures (e.g., high [OIII]/[OII] or low [O/H]) are seen in progressively
more luminous (massive) systems at higher redshifts.
