In this article we present two lexical decision experiments that examine the role of base frequency and of derivative suffix productivity in visual recognition of Spanish words. In the first experiment we find that complex words with productive derivative suffixes result in lower response times than those with unproductive derivative suffixes. There is no significant effect for base frequency, however. In experiment two, the same procedure was undertaken with pseudowords, showing that when they are composed by productive derivative suffixes they take longer to be rejected than when they are composed by unproductive derivative suffixes. Again, the role of base frequency fails to reach significance. These results endorse the view that derivative suffixes have a relevant role in visual recognition of complex words. According to our results, derivative suffixes create the conditions for taking a lexical candidate as a legal lexical entry and therefore they contribute decisively to the lexical decision.