A total of 24 healthy female and male volunteers (age 18 to 49 years old) will be recruited to participate in this study. Volunteers will be determined to be free of significant medical conditions as assessed by medical history, physical examination, and blood and urine tests. Volunteers will be randomly allocated to receive one of the four treatment sequence groups and, on each occasion, receive one of the following: Fresh Prograf (RLD), fresh generic tacrolimus, 10-30% crystallized generic (Low Crystal), and 40-60% crystallized generic (High Crystal) tacrolimus. There will be a minimum 2-week washout between treatments. On each occasion, healthy volunteers will be administered tacrolimus, 5 mg, as a single capsule orally on an empty stomach with approximately 240 mL of water. Blood samples will be collected from the indwelling venous catheter (∼10 ml) after 0.5, 1, 2, 3, 4, 6, 8, 12 and 24 hours after dosing. Subjects will be regularly monitored during this time. The volunteers will be allowed to eat a normal lunch 3 hours after taking their tacrolimus dose.