The immune system is the primary line of defense against infections and other things perceived as foreign to the body. Unfortunately, this immune system often fails to eliminate tumors or other cancerous growths. The drug diphenylcyclopropenone, or DPCP, modifies the immune system and has been shown to be effective in treating certain kinds of cancer. This study hopes to improve our understanding of how this drug helps create an effective immune response. In order to reach this goal, normal volunteers will be given the DPCP drug in the form of a gel or a placebo gel (gel without the active chemical) on a few small areas of skin. Then, biopsies will be taken of the skin at the sites where the active drug was placed. Also, small biopsies will be taken from opposite areas of skin which received placebo gel to serve as controls. The biopsied skin samples will then be studied by methods such as immunohistochemistry and microarray analysis which will help define the immune reaction caused by DPCP. The rationale for the study is to better understand how the immune system can be activated to produce cells that may fight infections or cancers.