The Hancock porcine xenograft valve was the first commercially prepared, quality-controlled tissue valve. The National Institutes of Health group began implantation of this valve in 1970 and reported on the first 5 years of their results, which was one of the longest follow-ups of that valve at that particular time. Since then there have been a number of centers that have had long-term experience with thousands of these valves. In retrospect, it is now clear that some of the conclusions made by the National Institutes of Health group have not come to pass, such as this valve being the "valve of choice" for all patients. "Valve of choice" is a relative term and may be one valve for one patient and another valve for another patient. This report was important in bringing together some of the first medium-term data and pointing out that, even in this valve, there was some small degree of thromboembolism. The paper also provided a historical look at the methods of data analysis that were in use in the early 1970s compared with those now used in 1991. Actuarial curves were not yet commonly used, nor were percent/patient-year linearized results. Valve types were mixed as well. Hemodynamic data, always a strong point of National Institutes of Health data analysis, were excellent. The use of this valve became a fairly standard device and has been retrospectively analyzed by a number of centers, suggesting that now it is better used in the older patient or in patients who cannot take warfarin sodium.(ABSTRACT TRUNCATED AT 250 WORDS)