Colour measurements of quasars are used to constrain the abundance and properties of intergalactic dust and the related extinction effects on high- z sources .
For Type Ia supernovae at z = 1 , we derive an upper limit on the possible dimming from intergalactic dust of \Delta m = 0.2 , ruling out the “ grey ” dust scenario as being solely responsible for the observed faintness of high- z SNIa .