This paper compares three methods to increase validity of case-control studies when two imperfect measurement tools are available to assess exposure. From simulated data, we show that point estimates of the relative risk, using only concordant dual responses, are always less biased than any other estimate. Because of the loss of power due to discarding discordant responses, the concordant response design is not efficient and is expensive. We show that a series response estimation, whereby all information is used but only dual positive responses are considered exposed, can be used to complement the interpretation of the less biased estimates. This approach is more interesting when exposure is rare and measuring it expensive.