Presidents Bok and Horner bade farewell to about 400 members of the Class of '79 at the annual Baccalaureate service in Memorial Church.
Bok spoke about the "crisis of the professions" to an audience of seniors in caps and gowns.
Specialization of professional fields has led to a "separation of professionals from the human beings they serve," Bok said.
"There are fewer doctors and lawyers with close and continuous relationships with their clients," he added.
Bok said the rapid growth of professional salaries and the greater demand for service fostered by technical progress might be responsible for the decline in public trust of professionals.
Horner praised the senior class for "questioning ethical issues within and without Harvard Square."
She told seniors to question all their assumptions and to "resist the temptation to replace old stereotypes with new ones."
The great tragedy of science is the slaying of the beautiful hypothesis by the ugly fact," she added.
Bok filled his speech with anecdotes, saying John Quincy Adams told his mother the "mere mention of the word attorney' incites the ire of others."
Bok said professions are facing confliets between their obligations to society and their clients as well as restrictions created by bureaucracy and government regulations.
"Institutions must try to conquer the vices of business by responding in new ways to the human needs of their clients and learn to serve them without trampling on the public interest," Bok said.
"Private institutions will have to either meet social needs in a creative way on their own or wait for government to impose them," he added.
The Baccalaureate Service also included readings by Robin B. Balthrope '79, Katie Forsman '79, Gary M. Barrett'79, Barbara A. Mullin '79 and Michael R. Eastman '79, as well as various hymns, and an invocation by Rev. Peter J. Gomes, Plummer Professor of Christian Morals and minister in Memorial Church.
Seniors spent the day showing their parents around Cambridge, and finished the day with a clambake at the Palmer Dixon tennis courts.