We present an analysis of the number density and spatial distribution of the population of millimetre galaxies (MMGs) towards 17 high-z active galaxies using 1.1 mm observations taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE) and the James Clerk Maxwell Telescope (JCMT). The sample allows us to study the properties of MMGs in protocluster environments and compare them to the population in blank (unbiased) fields. The goal is to identify if these biased environments are responsible for differences in the number and distribution of dust-obscured star-forming galaxies and whether these changes support the suggestion that MMGs are the progenitors of massive (elliptical) galaxies we see today in the centre of rich clusters. © 2011: Instituto de Astronomía.