  We report 250 GHz (1.2mm) observations of redshift > 3.8 quasars from the
Palomar Sky Survey (PSS) sample, using the Max-Planck Millimetre Bolometer
(MAMBO) array at the IRAM 30-metre telescope. Eighteen sources were detected
and upper limits were obtained for 44 with 3-sigma flux density limits in the
range 1.5-4 mJy. Adopting typical dust temperatures of 40-50K, we derive dust
masses of ~10^8-10^9 M_sun and far-infrared luminosities of order 10^13 L_sun.
We suggest that a substantial fraction of this luminosity arises from young
stars, implying star formation rates approaching 10^3 M_sun/yr or more. The
high millimetre detection rate supports current views on a connection between
AGN and star forming activity, suggesting a parallel evolution of the central
black hole and of the stellar core of a galaxy, although their growth-rate
ratio seems higher than the mass ratio observed in nearby galaxies. The
observed, exceptionally bright objects may trace the peaks of the primordial
density field, the cores of future giant ellipticals
