The study presented in this paper aimed to investigate the pattern of semantic priming effects, under masked and unmasked conditions, in the lexical decision task, manipulating type of semantic relation and associative strength. Three different kinds of word relations were examined in two experiments: only-semantically related words [e.g., codo (elbow)-rodilla (knee)] and semantic/associative related words with strong [e.g., mesa (table)-silla (chair) and weak association strength [e.g., sapo (toad)-rana (frog)]. In Experiment 1 a masked priming procedure was used with a prime duration of 56 ms, and in Experiment 2, the prime was presented unmasked for 150 ms. The results showed that there were masked priming effects with strong associates, but no evidence of these effects was found with weak associates or only-semantic related word pairs. When the prime was presented unmasked, the three types of relations produced significant priming effects and they were not influenced by association strength.