Malondialdehyde (MDA), a byproduct of non-enzymatic lipid peroxidation and prostaglandin biosynthesis, has been shown to be a weak frameshift mutagen in Salmonella mutagenicity assays. Because it is a dialdehyde, MDA can undergo self condensation to form polymeric products. It is possible that these condensation products are highly mutagenic and have contributed to previously reported estimates of MDA mutagenicity. We synthesized two major MDA polymerization products, (1) 2-(3'-oxo-1'-propenyl)-malondialdehyde [(MDA)2] and (2) 2,4-dihydroxymethylene-3-(2,2-dimethoxyethyl)glutaraldehyde [(MDA)3Me2] and tested their mutagenicity in the Salmonella frameshift tester strains hisD3052 and TA94 (hisD3052/pKM101). Analysis of the reversion rates revealed both (MDA)2 and (MDA)3Me2 to be weak mutagens, approximately equipotent to MDA. Although both (MDA)2 and (MDA)3Me2 are mutagenic, the fact that their formation is thermodynamically unfavorable under physiological conditions suggests they do not contribute significantly to the mutagenicity of MDA solutions.