This paper jointly considers some pieces of evidence regarding peculiarities of industries' structure which are often separately addressed. Italian industrial sectors are known to be characterized by a high proportion of small enterprises that suffers from constraints to growth. We look at the interplay of variables accounting for size, productivity and labor cost, and assess the relevance of labor force structure in determining the structure of cost for wage. We start by exploring the firm size-wage effect in Italian manufacturing sectors and investigate the extent to which such a trend is offset by a positive and counterbalancing relation linking together productivity and size. We investigate how size contributes to the wage differential within a firm on the earnings of distinct categories of employees. The empirical findings we present reveal that labor force structure matters in determining the wage cost structure of firms.