This thesis develops an explanatory model of the determinants of the purchase of Managerial Advisory Services (MAS) by an audit client from their auditor. The regression results show that variations in auditee characteristics result in variations in the purchase of MAS from the incumbent auditor. Auditee characteristics are shown to affect an auditee's purchase of MAS include: the size of the firm, the decentralisation of the auditee's organisation, whether the auditee's organisation is restructuring, the percentage change in the auditee' s board of directors, the growth in the auditee' s total assets, and the growth in the auditee's economic performance. The result is consistent with an auditee's purchasing MAS for a "legitimate motive", a response to an underlying auditee need for the MAS. The results support the proposition that an auditee's purchase of MAS from their auditor is undertaken to utilise the knowledge, both general and specific possessed by the auditor, in order to satisfy their underlying demand for MAS. The research contributes to the literature regarding the joint provision of MAS and audit services by the auditor.