The chemical synthesis of a series of poly-gamma-glutamyl metabolites of the experimental anticancer drugs 10-deazaaminopterin (10-DAAM) and 10-ethyl-10-deazaaminopterin (10-EDAAM) has been carried out by the solid-phase procedure. The synthetic products were identical with the poly-gamma-glutamyl metabolites of radiolabeled 10-DAAM and 10-EDAAM produced by normal mouse tissues with regard to elution volume from [(diethylamino)ethyl]cellulose columns and susceptibility to hydrolysis by human plasma folylpolyglutamate hydrolase. Poly-gamma-glutamyl metabolites with a glutamate chain length of up to four glutamate residues were detected in the tissues. The antifolate activity was evaluated with methotrexate (MTX) sensitive and MTX-resistant strains of Lactobacillus casei and Streptococcus faecium. In general, inhibitory potency decreases with increasing Glu chain length. However there are two exceptions. Addition of one Glu residue to 10-DAAM enhances its potency for MTX-resistant L. casei and addition of one Glu residue to 10-EDAAM enhances its potency for the MTX-sensitive L. casei. As shown earlier for MTX polyglutamates, polyglutamylation greatly enhances the inhibitory potency of 10-DAAM and 10-EDAAM for L. casei thymidylate synthase. MTX polyglutamates are 15-30 times more inhibitory than the corresponding 10-DAAM derivatives and 30-60 times more inhibitory than the corresponding 10-EDAAM derivatives. Polyglutamylation of 10-DAAM had little influence on its ability to inhibit L. casei dihydrofolate reductase; however, with 10-EDAAM, addition of one or two Glu residues enhanced its inhibitory potency 2.3-fold.