In radio, spokesperson plausibility is a resource that can better the efficiency of a message, and its assay demands the inquiry of how voice qualities affect the listener. The goals of this inquiry are to design and evaluate the fitness of a scale of radio spokesperson credibility, and to explore the effect of the phonoaesthetic function – that is, how a spokesperson’s gender, vocal pitch, accent and their interactions affect their credibility. The inquiry conducted a 2 × 2 × 2 experimental design via eight radio programmes in which a radio spot was inserted as stimulus material. The hypotheses were tested on a sample of 987 Spanish radio listeners, and the advertised service was blood donation. The results permitted the validation of a scale of spokesperson credibility, traditionally employed in audiovisual media, formed by three dimensions (attractiveness, expertise and trustworthiness), and supply several implications for the selection of a spokesperson for radio.