Abstract: The invention relates to a method for finding nucleotide synthesis inhibitors which have a better therapeutic window. An efficacious dose of a nucleotide synthesis inhibitor is administered to a mammal. The concentration of the nucleotide synthesis inhibitor in the blood of the mammal is observed and it is determined whether the nucleotide synthesis inhibitor has a half-life which is shorter than that of N-(4-trifluoromethylphenyl)-2-cyano-3-hydroxycrotonamide. The invention also relates to a method of using nucleotide synthesis inhibitors in the treatment of immunological diseases.