We present submillimetre ( submm ) continuum observations of a sample of some of the highest redshift quasars currently known , made with the SCUBA bolometer array on the JCMT .
12 of the sample have redshifts greater than five , and two have z \geq 6 ; the median redshift of the sample is 5.3 .
Two of the z > 5 objects are strong ( 6 \sigma ) detections , and are bright sources with S _ { 850 \hbox { \thinspace$ \mu$m } } > 10 mJy .
Another firm ( 5 \sigma ) detection is obtained for the z = 5.7 quasar SDSS J1044 - 0125 ; and SDSS J1306+0356 , at z = 6.0 , is detected with a signal-to-noise ratio \approx 4 .
We have obtained sensitive ( \sigma \approx 1.5mJy ) upper limits for much of the remainder of the sample , including the z = 6.3 quasar SDSS J1030+0524 .

Submm spectral indices measured for two of the sources ( \alpha \approx 3.3 ) are consistent with thermal reradiation from dust , rather than from synchrotron emission .
Sensitive upper limits at 450 \mu m imply that the dust is cool , requiring large dust masses ( 10 ^ { 8 - 9 } \hbox { $ \thinspace M _ { \odot } $ } ) to account for the observed fluxes— suggesting substantial prior star formation , even at z = 6 when the Universe was only 1.0Gyr old .