Purpose - The purpose of this research is to analyse the problems for occupational health and safety (OHS) regulators posed by agency work/leased labour (also known as labour hire in Australasia), using Australian evidence. Design/methodology/approach - The analysis is based on an examination of prosecutions involving labour hire firms along with other documentary records (union, industry and government reports and guidance material). The study also draws on interviews with approximately 200 regulatory officials, employers and union representatives since 2001 and workplace visits with 40 OHS inspectors in 2004-2005. Findings - The triangular relationship entailed in labour leasing, in combination with the temporary nature of most placements, poses serious problems for government agencies in terms of enforcing OHS standards notwithstanding a growing number of successful prosecutions for breaches of legislative duties by host and labour leasing firms. Research limitations/implications - Research to investigate these issues in other countries and compare findings with those for Australia is required, along with assessing the effectiveness of new enforcement initiatives. Practical implications - The paper assesses existing regulatory responses and highlights the need for new regulatory strategies to combat the problems posed by labour. Originality/value - The OHS problems posed by agency work have received comparatively little attention. The paper provides insights into the specific problems posed for OHS regulators and how inspectorates are trying to address them.