Since April 1990, data from the National Notifiable Diseases Surveillance System for 14 diseases have been published in a graphic format in the MMWR (Figure I, page 118) (1). The bar graph compares provisional reports for a 4-week period with the mean of 15 4-week totals (from the previous, comparable, and subsequent 4-week periods for the last 5 years) (2). Ratios that exceed national historical limits (calculated based on two standard deviations of the historical baseline) are indicated by striping in the bars. This report summarizes an evaluation of this new method.