Alginate genes are a group of genes which responsible for alginate production and regulation ([alg.sub.s] genes). The [alg.sub.s] genes validity and viability govern the alginate amount. Did our lung responsible for the mucoid conversion in P. aeruginosa? [H.sub.2][O.sub.2] has been used in this study to answer this question and to map the [alg.sub.s] genes validity and viability. [H.sub.2][O.sub.2] is one of the lung defense mechanisms during infections. [H.sub.2][O.sub.2] did not induce mucoid conversion in all P. aeruginosa tested strains. So other factors are included. In this study ten P. aeruginosa isolates out of many, half of them are mucoid while the other half is non-mucoid were investigated for their response to [H.sub.2][O.sub.2] at 30 and 37[degrees]C respectively. FT-IR were used to analysis the produced alginate. Temperature did not affect on the alginate production ability/inability but affect on their amount/time. However, temperatures become an effective factor in presence of [H.sub.2][O.sub.2]. Two non mucoid stains show mucoid conversion at 37[degrees]C in presence of [H.sub.2][O.sub.2] but not at 30[degrees]C. The maximum amount of alginate was produced by strain number one. The amount of the produced alginate has been increased from 0.009 to 0.24 g/l/h after adding [H.sub.2][O.sub.2] at 37[degrees]C. This study clearly addresses the role of [H.sub.2][O.sub.2] and the temperature as well as the [alg.sub.s] history. The history of [alg.sub.s] will be responsible for the amount of alginate produced during lung infection or after being induced with [H.sub.2][O.sub.2]. For the clinical isolates, we recommended using our mucoid-biotyping strategy for mapping the [alg.sub.s] genes viability and validity. Keywords: P. aeruginosa, mucoid, Alginate, H2O2, temperature.