People in high-risk neighbourhoods try to protect their friends, neighbours, relatives and others from the social and physical risks associated with sex and drug use. This paper develops and validates a community-grounded questionnaire to measure such 'intravention' (health-directed efforts to protect others). An initial ethnography, including life-history interviews and focus groups, explored the forms of intravention activities engaged in by residents of Bushwick (a high-risk New York City neighbourhood). Grassroots categories of intraventions were derived and questions developed to ask about such behaviours. Face validity and adequacy of the questions were assessed by independent experts. Pre-testing was conducted, and reliability and validity were assessed. An instrument including 110 intravention items was administered to 57 community-recruited residents. Analysis focused on 57 items in 11 domain-specific subscale. All subscales had good to very good reliability; Cronbach's alpha ranged from .81 to .95. The subscales evidenced both convergent and discriminant validity. Although further testing of this instrument on additional populations is clearly warranted, this intravention instrument seems valid and reliable. It can be used by researchers in comparative and longitudinal studies of the causes, prevalence and affects of different intravention activities in communities. It can benefit public health practitioners by helping them understand the environments in which they are intervening and by helping them find ways to cooperate with local neighbourhood-level health activists.