This study examines the effectiveness of R&D tax incentives using an unbalanced panel of 434 Canadian firms. Not all firms in the sample are R&D performers. A B-index summarizing the various tax incentives for R&D is constructed for each firm, taking into account individual ceilings in the use of the relevant tax incentives. A generalized Tobit model with fixed effects is estimated. A one percent increase in the federal tax credit to R&D yields an average of $0.98 additional R&D expenditure per dollar of tax revenues foregone (for firms with a ceiling in their use of federal tax credit). Using the same measure on firms which are not subject to a ceiling, we obtain $1.04. Tax transfers represent more than 80% of the cost of government support to R&D.