Despite a growing literature suggesting that the lyrics of music may have an emotional effect, there are as of yet no studies examining which elements of lyrics influence emotional experience. The present study explored the emotional effect of lyrics sung without a melodic accompaniment, examining whether the vocal expression or the semantic content of the lyrics had a greater influence on emotional state. A sample of 170 participants were presented four variants of sung lyrics, representing all possible combinations of vocal expression (happy; sad) and semantic content (happy; sad) condition, with emotional state being measured using the Brief Mood Introspection Scale (BMIS) following each presentation. A 2x2 repeated-measures ANCOVA revealed that, after controlling for familiarity with the song, both the emotional valence of the vocal expression and the semantic content influenced emotional experience, though the vocal expression did so to a greater magnitude. Therefore, the vocal expression of lyrics may have the dominant effect on emotions, though the semantic content still has a minor influence.