Variations in the drug use patterns of injection drug users (IDUs) can have important implications for public health efforts aimed at reducing drug abuse and the transmission of the human immunodeficiency virus. This article describes and compares the characteristics of IDUs living in four Ohio cities and compares African-American and White IDUs at a statewide level. Data from 2,001 IDUs who were recruited for the National AIDS Demonstration Research project between 1989 and 1991 in Columbus, Cleveland, Cincinnati, and Dayton were compared on a number of variables by city and by ethnicity using descriptive statistics and ANCOVA analysis. Significant differences among IDUs in the four cities exist for the use of alcohol, marijuana, cocaine, crack, heroin, speedball, other opioids, shooting gallery use, "safer" needle practices, treatment history, and self-help participation. Differences by ethnicity emerged on all variables except marijuana use, overall injection frequency, and incarceration experience. The results suggest that dramatic differences exist between African-American and White IDUs, and among IDUs in cities relatively close together, regardless of ethnicity. These findings should be considered when developing policy and programs for prevention and treatment activities targeting IDUs.