Available experimental evidence on possible human health effects from exposure to high voltage ac transmission line electromagnetic fields is contradictory and inconclusive. Yet, in several states, growing public concern is regulatory action. A number of alternative technologies are available to control human exposure to these fields. This paper looks briefly at the available evidence on health effects, estimates the costs of possible control technologies, and then performs an analysis to bound the region of appropriate control strategies for electric field exposures for representative 500 and 765-kV ac transmission lines. Results are presented parametrically in the key variables. Both the value and the potential societal costs of the analytical approach we take are discussed.