IN THE 1970S THERE was a noticeable increase in the amount of preferred stock issued by utility companies. During this period the historically positive yield differential between high grade preferred stocks and high grade corporate bonds turned negative. A substantial fraction of the demand for preferred stock has come from casualty and stock life insurance companies [10]. Much of the corporate demand for preferred stock may be attributed to the 85 percent exclusion of preferred dividends from net income for federal income tax purposes. Insurance companies must follow the valuation rules of the National Association of Insurance Commissioners (NAIC). For example, bonds may be carried at amortized original cost (book value) if they are investment grade (equivalent to Moody's Baa or higher), but they have to be carried at a lower value if they have lower ratings. Common stock is carried at market price. The NAIC recently adopted a rule permitting insurance companies to carry sinking fund preferreds at book value rather than marking them to the market. The 1979 edition of the Valuation of Securities: Procedures and Instructions booklet published by the NAIC allows preferred stock held by property and casualty companies to: Commencing with the December 31, 1978 Annual Statement, be valued for statement purposes at cost, providing the is subject to a 100% mandatory sinking fund ... over a period not longer than 40 years from the date of issue [11]. Holding assets which are accounted for at book value rather than market value reduces the variance of reported equity. The benefit of this provision for insurance companies is that during a period of rising interest rates, sinking fund preferred stock held by insurance companies will not contribute to erosion of reported asset base and balance sheet equity. It is likely that in some instances the provision would enable insurance companies to continue to write new policies at a growth rate that would not otherwise be possible due to state statutes which limit the maximum value of policies written in relation to balance sheet asset value. Whether or not bookkeeping rules have a significant impact on security prices has long been an interesting question [4] [6]. This paper examines the impact of the change in NAIC rules upon the pricing of preferred stock.1