The efficacy of current landfill gas and radon mitigation measures for the prevention of ingress of organic vapours was investigated by the study of four houses situated on contaminated land in North West England. The chemical present in the ground of greatest concern for health due to exposure to vapour in the indoor air was hexachlorobutadiene (HCBD) and the concentration of this compound was used to assess the effectiveness of the remedial measures. A two stage remediation was undertaken. For a house with a solid floor the top surface of the floor was sealed and then for the second stage a fan was used to pressurise the soil gas beneath the house. In a house with a suspended timber floor, extra air bricks were installed to increase ventilation of the floor void and then a fan to further increase air exchange in the void. HCBD in air was monitored by both pumped and diffusive sampling methods. Control houses were also monitored that were not subject to remediation. It is concluded that the remedial measures used for radon protection of a suspended floor have the potential to reduce indoor HCBD concentrations by about 80%, at least in downstairs rooms (where initial levels were highest). The two techniques used for properties with solid floors do not appear to be as effective, and no benefit at all was seen without making allowances for changes in concentration that occurred in the control house over the same period. Further work is required to test the efficacy of the techniques over a longer period and under different circumstances of type of contamination and building characteristics.