Book excerpt: The Securities and Exchange Commission (SEC) has mandated new disclosure requirements in Form 8-K, which became effective on August 23, 2004. The SEC expanded the list of items that have to be reported and accelerated the timeliness of these reports. This study examines the market reactions to 8-Ks filed under the new SEC regime and investigates whether periodic reports (10-K/Qs) became less informative under the new 8-K disclosure rules. We observe that the newly required 8-K items constitute over half of all filings and that most firms disclose the required items within the new shortened period (four business days). We find that all disclosed items (old and new) are associated with abnormal volume and return volatility around both the event and the SEC filing dates, and some items have significant return drifts after the SEC filings. Surprisingly, we find that the information content of periodic reports has not diminished by the more expansive and timely 8-K disclosures under the new guidance, possibly indicating that investors may use periodic filings to interpret the effects of material events that had been disclosed earlier.