The principal objectives in this paper are to assess and to build upon the recently published research of Ang et al. (2000) making a pioneering attempt to estimate equity agency costs in a large cross-sectional sample of smaller, non- publicly traded companies in the United States. The present research employs panel data for 871 manufacturing SMEs legally organised as proprietary companies, taken from the Australian federal government's Business Longitudinal Survey conducted over four financial years from 1994--1995 to 1997--1998. The two proxies for equity agency costs that are trialed -- operating expense ratio and asset turnover ratio -- both appear lower in more complex agency relationships. It is also found that greater enterprise growth is significantly more evident amongst SMEs with more complex agency relationships. Thus, it is possible that observed differences in values for the two equity agency cost proxies are not the direct consequence of differences in management and ownership structures; but, rather, of differences in the experience of enterprise growth, possibly enabled to some degree by the management and ownership structures adopted. This raises the question of whether, in fact, operating expense ratio and asset turnover ratio can be reliably used as proxies for equity-related agency costs in SME research.