Addition of glyoxylate to the culture media of P. fluorescens causes: a strong plastogenic effect with the formation of giant cells and an increased growth rate; a total inhibition of biosynthesis of pigment. Succinate is rapidly utilized by P. fluorescens; if associated with an NH3 source, pigment production surpasses that in media based on asparagine. The early appearance of pigment with sifccinate suggests its direct participation in the formation of a pigment precursor. The differences in chromogenic effect between glycine and its dipeptide are attributed to the kinetics of bacterial metabolism of P. fluorescens.