A medicament for inhibiting growth of human and animal cells comprising: (1) a cell growth inhibitory amount of a one or more growth inhibitors comprising synthetically prepared sphingosine, synthetically prepared N-methyl-sphingosine or pharmaceutically acceptable salts thereof; and (2) a pharmaceutically acceptable carrier, diluent or excipient. A method for inhibiting growth of human and animal cells in vivo comprising contacting said cells with a cell growth inhibitory amount of one or more growth inhibitors comprising synthetically prepared sphingosine, synthetically prepared N-methyl-sphingosine or pharmaceutically acceptable salts thereof. A medicament for inhibiting growth of human and animal cells comprising: (1) A cell growth inhibitory amount of one or more growth inhibitors comprising sphingosine prepared from naturally occurring sphingolipid, N-methyl-sphingosine prepared from naturally occurring sphingolipid or pharmaceutically acceptable salts thereof; and (2) a pharmaceutically acceptable carrier, diluent or excipient. A method of inhibiting growth of human and animal cells in vivo comprising contacting said cells with a cell growth inhibitory amount of one or more growth inhibitors comprising sphingosine prepared from naturally occurring sphingolipid, N-methyl-sphingosine prepared from naturally occurring sphingolipid or pharmaceutically acceptable salts thereof.