Under a Relational Frame Theory (RFT) framework, researchers have investigated the role of deictic relational responding (perspective-taking) in the analysis of self in relation to others, place, and time. The aim of the current research was to develop IRAPs that targeted deictic relational responding with regard to the mental states of self and others. This was pursued in a series of experiments that employed a novel version of the IRAP, known as the Natural Language-IRAP (NL-IRAP). The use of the NL-IRAP allowed for the presentation of relatively complex statements that required participants to infer the thoughts or beliefs of others on a trial-by-trial basis within the IRAP. Across a sequence of six experiments, a 'selffocused IRAP' required participants to respond to both positive and negative statements about themselves, whilst an 'other-focused IRAP' required participants to respond to similar statements about others. Experiments 1 and 2 investigated perspective-taking with regard to an unspecified other. Experiments 3-6 investigated perspective-taking with regard to a specified other, with the specified relationship between self and other manipulated across experiments. The results of Experiments 1 and 2 indicated that the other-focused IRAP produced overall bias scores that were significantly stronger than responding to the selffocused IRAP. Interestingly, non-significant differences were recorded across Experiments 3-6 when other was specified. The findings obtained across the six studies highlight potentially important limitations in the use of the NL-IRAP as a measure of perspective-taking.