Malcolm Fraser appointed Lynch Treasurer in 1975. When the Treasury portfolio was split into Treasury and Finance in December 1976, Lynch held both portfolios. He is noted for using the expression "rubbery" to describe some of the estimates in his 1977 Budget Speech, leading to the use of the expression "rubbery figures" in Australian political debate. He was forced to resign from the ministry on 19 November 1977 when it became known that he was using a family trust to minimise his tax obligations, which was perceived as a conflict of interest. He was replaced as Treasurer by John Howard and as Minister for Finance by Eric Robinson. An official inquiry found that he had done nothing illegal or improper, and he returned to the ministry in December, as Minister for Industry and Commerce.