Maternal mortality is high in Pakistan, particularly in the rural areas which have poor access to health services. We investigated the risk factors associated with maternal mortality in sixteen rural districts of Balochistan and the North-West Frontier (NWFP) provinces of Pakistan. We designed a nested case-control study comprising 261 cases (maternal deaths reported during last five years) and 9135 controls (women who survived a pregnancy during last five years). Using contextual analysis, we estimated the interactions between the biological risk factors of maternal mortality and the district-level indicators of health services. Women under 19 or over 39 yr of age, those having their first birth, and those having a previous history of fetal loss were at greater risk of maternal death. Staffing patterns of peripheral health facilities in the district and accessibility of essential obstetric care (EOC) were significantly associated with maternal mortality. These indicators also modified the effects of the biological risk factors of maternal mortality. For example, nulliparous women living in the under-served districts were at greater risk than those living in the better-served districts. Our results are consistent with several studies which have pointed out the role of health services in the causation of maternal mortality. Many such studies have implicated distance to hospital (an indicator of access to EOC) and lack of prenatal care as major determinants of maternal mortality. We conclude that better staffing of peripheral health facilities and improved access to EOC could reduce the risk of maternal mortality among women in rural Balochistan and the NWFP.