Six patients are enrolled sequentially into each of eight different dose levels and the drug is administered by mouth at least 60 minutes before meals according to the following schedule: Day 1: One-quarter of total assigned daily dose. Patients receive the dosage in the hospital as either an inpatient or outpatient and are observed for 12 hours, during which time they are evaluated and blood is drawn for pharmacokinetic studies. Patients return at 24 and 48 hours for a limited physical examination and additional pharmacokinetic studies. Days 4 - 31: Total assigned daily dose, one-quarter 4 times a day. Patients are observed for at least 5 days in the hospital following the start of this part of the program, during which time clinical, laboratory, and pharmacokinetic information is obtained in order to establish baseline values. After the 6th day, patients are evaluated with a complete physical exam, urinalysis, and laboratory studies once a week and a limited physical exam and brief laboratory studies 3 times a week. At each of the eight dose levels, the second and third patients receive their first dose only after the first patient has been followed for 72 hours after receiving the first dose. Patients 4, 5, and 6 begin treatment only after patients 2 and 3 have completed 14 days of the four-part total dose. Patients are treated on an outpatient basis, with 5 to 6 days spent in the hospital for evaluation.