a rapamycin dimer of general formula ## str1 ## wherein a is -- n --, -- n ---- m --, -- n ---- m --, ## str2 ## substituted alkyl , substituted alkenyl , substituted alkynyl , and substituted aromatic ; n = 1 - 10 , m = 1 - 10 and n = m or n ≠ m or a pharmaceutically acceptable salt thereof , which is by virtue of its immunosuppressive activity is useful in treating transplantation rejection host vs . graft disease , autoimmune diseases , and diseases of inflammation .