The gene expression level for immune system genes was evaluated at different lifecycle stages in the white shrimp (Litopenaeus vannamei). The gene-coding pattern recognition protein, -glucan binding protein-high density lipoprotein (BGBP), from haemocytes, the effector proteins peroxinectin and clotting protein (CP), the antibacterial proteins Lysozyme, Penaeidin 3 and prophenoloxidase (proPO), and the small heat-shock protein 10 were studied. The expression of BGBP was detected from the Nauplii 3 substage and beyond (except for PL1). Peroxinectin and CP were constitutively transcribed throughout the different substages. Lysozyme, Penaeidin and proPO were also detected throughout the experimental stages (except eggs and nauplii). Lysozyme was transcribed during most of the shrimp substages, from Zoea 2 and beyond. Penaeidin 3 exhibited the lowest expression level of the genes evaluated; however, its transcription was similar to those of adults from post-larvae 11 and forward. proPO was higher transcribed during last post-larval substages. Heat-shock protein-10 was detected in all shrimp substages and exhibited higher expression at the PL substages compared to the first larval substages. Evidence suggests that the shrimp immune system is partially activated from the early larval substages, but is not completed until the shrimp have undergone the metamorphic substages.