UNIVERSITA' DEGLI STUDI ROMA "TOR VERGATA"We study the implications of having diferent sources of nominal rigidities on the relationship between productivity growth and shocks volatility in a model with procyclical R&D and imperfect competition in goods and labour markets. We show that the efects of uncertainty on long-term growth not only depends on the source of fluctuations, as recent literature shows, but also, and crucially, on whether prices and/or wages are rigid.