Randomized, double-blind. Patients at eight centers were assigned to receiving for six months a daily dietary supplement of fish oil (ten 1.0-g capsules containing 80.6 percent ethyl esters of omega-3 fatty acids providing 4.1 g eicosapentaenoic acid [EPA] and 2.8 g docosahexaenoic acid [DHA]) or to a control group receiving corn oil. The high dose of fish oil approached the intake of the Greenland Inuits and was chosen with the hope of overcoming any antagonistic effects of other fatty acids competing with those of EPA or DHA, such as arachidonic acid or saturated fats. Two weeks prior to PTCA, patients began to take the capsules. Aspirin was initiated 12 hours prior to PTCA and continued for six months. Dietary counseling was provided prior to the two week intervention. Upon admission for PTCA and one week following PTCA, expanded dietary counseling and instruction were given. Patients were telephoned monthly to reinforce dietary information which included the American Heart Association Phase I diet to reduce total fat to 30 percent of total energy. Diet was not rigidly controlled. Recruitment began in August 1989 and ended in September 1992. Patients exited from the trial upon completion of the protocol, including a final set of evaluations at six months. The primary endpoint was presence or absence of restenosis as defined by angiography six months after PTCA. The trial was extended without additional funds through June 1994 to allow data analysis.