This dissertation examines the reaction of common stock prices to changes in bond ratings by Moody's Bond Service. The question is whether an announcement of a re-rating by Moody's is new information. There are only two studies of stock price reaction to bond changes and the results are conflicting. Pinches and Singleton (1978) [PS] concluded that any reaction comes well before the re-rating. Griffin and Sanvicente (1982) [GS] found that their portfolio test indicated that rating changes do convey new information. This was particularly true for downgradings. Both studies used monthly data and neither performed a statistical testing of residual reversals. PS provided a graph of the residuals which indicated the presence of a reversal trend. GS provided no information on this topic. This study, using daily data and the cumulative prediction error technique, finds that bond re-ratings offer new information. The results indicate that the market only partially anticipates the bond change. For the downgrades, the excess return on the announcement day is .6% which is statistically significant. The residuals reverse after the announcement day, but are not statistically significant. The upgrades do not have a significant reaction on the announcement day, but have a statistically significant negative reaction from day 1 to 10. The cumulative residual for days 1 to 10 is -2.8% with a test statistic of -3.85. This study finds as PS that there is some anticipation for both upgrades and downgrades. It extends their work by statistically testings the reversals after the announcement date and by testing the announcement day effect. There is significant abnormal return for the downgrades on the announcement day and the upgrades have a significant reversal in their residuals from day 1 to 10. This provides both support and extension of Griffin and Sanvicente's results and suggests that Moody's is offering the market new information.