Accounting information is subject to two different influences: market pressures and pressure from regulatory bodies. This paper provides an empirical analysis of the influence of both these forces on information disclosure by Spanish firms. To test hypotheses concerning the influence of regulation, annual reports of three different years for 49 companies have been analysed. Given that new Spanish accounting rules have been in force since 1990, annual accounts of a sample of quoted companies have been analysed for the period 1989-1991. In order to consider the influence of positive accounting theory, several characteristics relating to company attributes were selected and tested empirically for the sample of 49 companies. The information disclosed by the sample companies was measured through an information index, based on a list of 50 items of information, and it was regressed on the variables related to company characteristics. The influence of regulation was analysed through a panel data analysis including time effects. The results suggest that time as a surrogate for regulation explains the level of information disclosure, although it does not influence the amount of voluntary information disclosed. However, several firm characteristics were also found to influence the level of disclosure, namely size, auditing and stock exchange.