Since August 1988 an increasing proportion of the executive functions of government in the United Kingdom have been devolved to executive agencies. Transfer to an executive agency involves a period of uncertainty during which the options of elimination or transfer to the private sector are considered, followed by a marked change in management style and further periods of uncertainty when the agency's function is reconsidered for transfer to the private sector. This paper examines the effects of this major organisational change and consequent job insecurity on the health status of a cohort of 7419 white-collar civil servants by comparing groups either exposed to or anticipating exposure to this stressor, with controls experiencing no change. Compared with controls, men both already working in and anticipating transfer to an executive agency experienced significant increases in health self-rated as "average or worse", longstanding illness, adverse sleep patterns, mean number of symptoms in the fortnight before questionnaire completion, and minor psychiatric morbidity. Significant relative increases in body mass index were seen in both exposure groups while exposure to agency status was also associated with significant relative increases in blood pressure. Health-related behaviours, where they differed between exposure and control groups, tended to favour those in the exposure groups. Compared with controls, women in both exposure groups reported small increases in most self-reported morbidity measures and most clinical measurements, accompanied by slight beneficial changes in some health-related behaviours and small adverse changes in others. Significant relative increases were seen in mean number of symptoms, and ischaemia among women anticipating exposure and in body mass index among those exposed to agency status. Policy makers should be aware of the wider consequences of job insecurity when considering the efficiency of changes in employment policy.