Tenure practices in science and engineering (S/E) departments in universities and 4-year colleges with tenure systems were estimated, based on a 1978-79 survey of member institutions of the Higher Education Panel of the American Council on Education. The survey findings were designed to help assess the effect of the tenure system on the number of faculty openings for new doctorates. Of the faculty openings available to recent doctorates, about 4 percent of the full-time S/E positions became vacant as the result of the failure of faculty to earn tenure or the expiration of nontenure-track openings. In addition, 2 to 3 percent of faculty positions opened due to retirement, other voluntary separations, and death. Growth in the number of faculty positions was the other major source of openings, accounting for approximately 4 percent of the full-time S/E positions. The greater the proportion of faculty who hold tenure, the smaller the number of potential openings for recent doctorates. About two-thirds of the 123,000 full-time S/E faculty at universities and 4-year colleges held tenure, another one-fourth were not tenured but in tenure-track positions, and about 1 in 14 were in nontenure-track positions. Data are also provided on tenure approval rates, reconsideration rates for those denied tenure, and pretenure probationary periods. Information is provided on tenure status and tenure decision outcomes of S/E faculty by field, institutional level, and type of institution. If the number of full-time faculty does not increase because of declining college enrollments, the tenure system may be an important source of openings for new faculty, if no major changes occur in tenure practices. (SW)