Prostate specific antigen (PSA) is the premier biomarker for diagnosis and monitoring of prostate cancer. PSA is a trypsin-like serine protease and belongs to a family of related genes which are known as the kallikrein-related peptidases. The family includes 15 members, of which 12 are trypsin-like and 3 are chymotrypsin-like. The image represents an imaginary structure of PSA (also known as KLK3) looking at one of its substrates (upper right). This work was created in July 2009 in Asian calligraphy style (monoprint, block printing ink on Whatman paper). The complete work includes imaginary structures of all 15 kallikreins and is currently displayed in the office of Dr. Eleftherios P. Diamandis, Mount Sinai Hospital, Toronto, Canada.