二氢叶酸还原酶缺乏症：一种因叶酸代谢障碍而发生的遗传性氨基酸病，致使叶酸转化成四氢叶酸减少，按四氢叶酸缺乏程度可引起自发流产或死胎，幸存婴儿不能健康成长，并患重症巨幼红细胞性贫血。用甲酰四氢叶酸(folinic acid)治疗有效- 2,4-D
- 2,4-dichlorophenoxyacetic acid
- 2,5-dimethoxy-4-methylamphetamine
- 25-hydroxycholecalciferol
- 25-hydroxyergocalciferol
- 2-acylglycerol O-acyltransferase
- 2-aminoadipate transaminase
- 2-aminoethanol
- 2-deoxy-D-glucose
- 2-oxoglutaric acid
- 2-oxoisovalerate dehydrogenase (lipoamide)
- 2-PAM
- 2-phosphoglycerate
- 2-phosphoglyceric acid
- 3,4-benzpyrene
- 3,4-dihydroxyphenylalanine
- 3,4-dimethoxyphenylethylamine
- 3',5'-cyclic-GMP phosphodiseterase
- 3,5-diiodothyronine
- 3-hydroxy-3-methylglutaryl CoA(HMG CoA) lyase deficiency
- 3-hydroxyacyl-CoA dehydrogenase
- 3-hydroxybutyrate dehydrogenase
- 3-hydroxyisobutyryl-CoA hydrolase
- 3-hydroxyisovaleric acid
- 3-ketoacyl-CoA thiolase