Mutants of Arabidopsis thaliana were identified by screening pedigreed M3 seed collections from EMS-treated plants for changes in fatty acid (FA) composition. The FA phenotypes of the most dramatic mutants are as follows: G30 and 1E5 (allelic) lack linolenic acid (18∶3) and are elevated in linoleic acid (18∶2); 4A5 is deficient in 18∶2 and 18∶3 and fourfold increased in oleic acid (18∶1); 9A1 lacks all FAs > C18 and is twofold increased in 18∶1; 1A9 is twofold increased in palmitic acid (16∶0) and decreased by one-half in 18∶1; 2A11 is two-to threefold increased in stearic acid (18∶0) and decreased by one-half in 18∶1. Based on segregation of F2 selfed plants derived from crosses to wild type, all of these phenotypes are the result of single gene mutations.