This study examined previous research the investigated the effective use of DNA testing in police investigative work and found that DNA testing was effective in solving property crimes; that the clearance rates for most crime types was positively correlated with the size of the local DNA database; that DNA testing sometimes had large, positive effects in police investigations; and that one study found that DNA testing had a negative effect on homicide investigations. The objective of this study was to examine previous research on the effectiveness of DNA testing as part of routine police investigative practices compared to other more traditional forms of investigation. The review examined five studies that estimated the effect of DNA testing as part of the investigative phase of a criminal case on a criminal justice system outcome. The findings indicate that DNA testing can be a valuable tool when used to investigate a broad range of crime types. Study limitations are discussed. References and tables