In this paper, we present evidence that the cross-section of UK expected stockreturns is positively related to RD activity. The association between returns andRD activity is significant even after controlling for ME and BM. The cross-sectional results are consistent with intangible assets resulting from research anddevelopment activities having higher risk than tangible assets.The results from time series analysis suggest that allowing for research anddevelopment activity in constructing factor models of returns can be important.The explanatory power of factor models generally improves after controlling forRD activity, particularly for portfolios of firms with no RD activity. This resultcan be explained by the three factors in the Fama and French model partiallycapturing effects associated with research and development activity. Inclusion o