SEVERAL ENIGMAS about the mechanism of valvular endocarditis still exist. Why such an entity prevails at all requires elucidation. The relation of vegetations on the valve to an underlying interstitial valvulitis and of the bacterial to the nonbacterial vegetation is still moot. Do the bacteria reach the valve via the interstitial capillary bed or as a deposit directly upon the surface of the valve? No experimental technique has yet reproduced the human forms of chronic distorting valvulitis, as in mitral stenosis. Bacterial endocarditis has been produced experimentally but by procedures which do not even mimic the conditions existing in the human. The following concept is presented for the origin of bacterial endocarditis. An underlying, prior, interstitial, edematous, and cellular valvular distortion occurs initially. This alteration in the valve substance is accompanied in localized areas of the valve by platelet vegetations, with and without fibrin and occasionally with collagen alteration and