Abstract: Sarcosine and certain sarcosine derivatives, specifically N-low alkyl glycines with 1 to 4 carbon atoms in the N-alkyl part, their acid amides and sarcosine anhydride exhibit a tumor-inhibiting effect alone for themselves and mixed with one another, as well as a synergistic effect in combination with other tumor-inhibiting compounds, in particular antineoplastic alkylating compounds, intercalating substances, antimetabolites and plant substances.

Abstract: This invention relates to compounds having the formula: ##STR1## wherein R.sub.1 and R.sub.2 are selected from the group consisting of hydrogen, acyl, trifluoroacetyl, straight chained and branched alkyl groups with up to 6 carbon atoms, such alkyl groups with up to 3 substituents selected from the group consisting of OH, OSO.sub.2 CH.sub.3, COOH, COOR, CONH.sub.2 and Hal, where R is an alkyl group with up to 6 carbon atoms, and R.sub.1 and R.sub.2 together form a heterocyclic ring containing 4 to 6 carbon atoms and optionally further heteroatoms and such rings with up to 3 substituents selected from the group consisting of lower alkyl, OH, COOH, COOR, CONH.sub.2, where R has the above meaning, the chloroethyl nitrosoureido group and Hal, and Hal is selected from the group consisting of chlorine and fluorine, which heterocyclic ring is not the para-methyl piperazine group, said nitroso ureas having a tumor inhibiting effect.