The Nucleic Acid Chemistry Shared Resource provides DNA sequencing support to the Cold Spring Harbor Laboratory Cancer Center. The resource operates two Applied Biosystems ABI377 DNA sequencers. One of these is operated as a full service instrument, the second as a shared instrument. For the full service instrument, investigators give DNA templates to the operator who carries out sequencing reactions and gives the data back to the investigator. Users of the shared instrument carry out their own sequencing reactions and analyze their samples on the shared instrument. This arrangement provides flexible access to DNA sequencing technology to the Cancer Center. This facilitates the many projects that require some amount of DNA sequencing support.