Prior research has failed to reach consensus on which variables explain private-sector research and development (R&D) spending. This study extends prior research explaining R&D spending of firms in the US private sector by regressing R&D intensity on a number of tax and organizational variables. COMPUSTAT data from 113 firms in 1994 are used to estimate the effects of the variables on R&D intensity (used interchangeably with R&D activity). Ordinary least square estimates indicate that firms that were eligible for the R&D credit had higher R&D activity than firms that were ineligible. R&D intensity is a decreasing function of both capital intensity and the debt to capital ratio. Neither management stockholding nor diversification strategy meaningfully influenced R&D activity. The reported results have implications regarding US tax policy towards the tax subsidy for R&D. The results also help to clarify prior findings regarding a number of organizational variables on R&D intensity. One implication of these results for US tax policy is that private sector R&D intensity can be meaningfully influenced by the level of tax subsidy.