This study was undertaken in a system of chick embryo liver cells incubated in Earle's Basal Salt Solution with hormones. Impairment of induction of Δ-aminolevulinic acid synthase (ALAS) by allyl-isopropylacetamide (AIA) was observed in the presence of glucose. Fructose and various gluconeogenic substances including gluconeogenic amino acids had a similar effect. Leucine, which is purely ketogenic, did not influence induction of ALAS. SH-containing amino acids increased induction of ALAS by AIA. The glucose analogues 3-0-methylglucose and 2-deoxyglucose did not impair induction of ALAS by AIA. The inhibitory effect of glycerol, fructose, and glycine was not affected by 3-0-methylglucose but was reversed by 2-deoxyglucose. The results indicate that the salutory effects of proteins on acute attacks of hepatic porphyria are probably caused by their gluconeogenic properties and that glucose-6-phosphate, or a metabolite of glucose-6-phosphate that is not in the glycolytic pathway, is the active agent that leads to the glucose-like effect.