Spirochete-like organisms were first detected in human feces in 1884. In the century since that observation an appreciable amount of epidemiologic and morphologic information has been published; nevertheless, it is not known how many species of cultivable human intestinal spirochetes exist, nor is the role of these organisms in health and disease known. Recent advances in microbiologic techniques, coupled with the recognition that the rate of carriage of such spirochetes in certain populations is approximately 30%-40%, should provide the impetus for careful scientific study of these organisms and of their importance-if any-to human health.