It is well-known that price- and quantity-based regulation approaches provide different investment incentives. But usually, only the effect on the level of investment is studied. In this paper, we show that under uncertainty, they also lead to the adoption of different technologies due to the disparate risks that a regulated firm is exposed to. Different regulatory instruments induce different technologies and this effect cannot be compensated by varying the design of the instruments. Furthermore, price-based instruments lead to the adoption of a socially suboptimal technology, so that the inclusion of technology choice provides a bias in favor of a quantity-based regulation compared with Weitzman's (Weitzman, M.L., 1974. Prices vs. quantities. Review of Economic Studies 41; 477-491) criterion. (C) 2007 Elsevier B.V. All rights reserved.