Gudjonsson developed two scales to measure interrogative suggestibility: Gudjonsson Suggestibility Scales I and 2 (GSS I and GSS 2; Gudjonsson, 1984a; 1987c). The aims of the present thesis were to examine issues related to the reliability and validity of these scales. Three studies are presented. Study I assessed the effects of two interviewer styles on measures obtained on the GSS 1. The hypothesis was that a generally abrupt demeanour adopted by the interviewer would lead to higher scores than a friendly demeanour. Results showed that participants tested in the Abrupt condition gained higher scores on two of the post-feedback GSS measures than those tested in the Friendly condition. It was concluded that post-feedback scores may be more sensitive to social aspects of suggestibility than responses to leading questions. Study 2 assessed the effect of the same interviewer demeanours on a sample of adolescents, a more vulnerable population (e. g. Richardson, Gudjonsson, & Kelly, 1995). It was hypothesised that the abrupt demeanour would produce higher GSS I scores, than a friendly demeanour and that this difference would be more marked than that found for normal adults. Results did not support the hypothesis. Scores were lower in the Abrupt condition; this difference was significant for post-feedback responses to leading questions. It was concluded that results provided further evidence that GSS scores are not readily predictable. Study 3 aimed to investigate indicators of "faking bad" on the GSS. It was hypothesised that participants instructed to fake suggestibility would demonstrate a unique scoring pattern. Results supported the hypothesis. It was concluded that an elevated pre-feedback score in the absence of any other raised scores may indicate malingering on the GSS. Issues related to the reliability and validity of the scales are discussed.