Abstract: A process for preparing biological material for implant in mammal's cardiovascular system, respiratory system or soft tissue is disclosed. The process comprises:(1) isolating from a suitable donor a desired tissue sample of the biological material;(2) extracting the tissue sample with an hypotonic buffer solution at a mild alkaline pH, the buffer solution including active amounts of proteolytic inhibitors and antibiotics;(3) extracting the tissue sample with a buffered solution having a high concentration of salt, the solution being at a mild alkaline pH and including a non-ionic detergent with protease inhibitors and antibiotics;(4) subjecting tissue sample to enzymatic digestion in a buffered saline solution, the enzymes consisting of purified protease-free dioxyribonuclease and ribonuclease;(5) extracting the tissue sample with an anionic detergent at a mild alkaline pH; and(6) storing the tissue sample in physiologic buffered solutions.