Thirty-eight ninhydrin-positive compounds (NPCs) were detected in the serum of wild, controlled-diet and starved lobsters Homarus americanus (Milne Edwards). Glycine, proline, alanine, taurine, serine, glutamic acid, ornithine, and glutamine comprised approximately 82% of the total serum NPC concentration in wild and starved lobsters and 70% in fed lobsters. The urea cycle intermediates arginine, citrulline, ornithine, and urea were detected in many samples. The following NPCs, previously unreported in lobster haemolymph, were detected as well: β-alanine, α-aminoadipic acid, α -amino-n-butyric acid, γ-aminobutyric acid, ammonia, anserine, as-paragine, cystathionine, cysteic acid – phosphoserine, ethanolamine, glycerophosphoethanol-amine, hydroxyproline, 1- and 3-methylhistidine. Starved lobsters showed pronounced reductions in serum NPC concentrations relative to those of fed lobsters. Starvation caused an apparent increase in the serum concentrations of the methylhistidine isomers and glycerophosphoethanolamine.