  We present the results of a narrow-band survey of QSO fields at redshifts
that place the [OIII](5007) emission line in the 1% 2.16micron filter. We have
observed 3 square arcminutes and detected one emission line candidate object in
the field around PC 1109+4642. We discuss the possibilities that this object is
a star-forming galaxy at the QSO redshift, z_em=3.313 or a Seyfert galaxy. In
the former case, we infer a star formation rate of 170 Msun/yr for this
Kprime=21.3 object. The galaxy has a compact but resolved morphology, with a
FWHM=0.6arcs, or 4.2kpc at z=3.313 (H_0=50 km/s/Mpc and q_0=0.5). The comoving
density of such objects in QSO environments appears to be 0.0033Mpc^3,
marginally lower (<= 3sigma) than the density observed for Halpha-emitters in
absorption-line fields at z~2.5, but similar to the density of Lyman Break
Galaxies at z~3. If on the other hand, most of the line emission is [OIII] from
a Seyfert 2 nucleus at z=3.31, then the high inferred volume density could
imply a large evolution in the Seyfert 2 luminosity function from the current
epoch. We find the field containing the object to also contain many faint
extended objects in the Kprime image, but little significant excess over the
expected number-magnitude relation. We discuss the implication of the emission
line being a longer wavelength line at a lower redshift.
