This paper proposes an approach to determine the level of Pseudomonas spp. in milk, based on the evaluation of the content of oxygen and carbon dioxide produced in the head-space of sealed vials; the research was divided into two phases: model building and preliminary validation. Three different strains of Pseudomonas spp., Ps. putida (wild strain) and Ps. fluorescens (wild and a collection isolates), were used as targets. Data of CO2 and O2 were modeled through a modified positive (CO2) or a negative Gompertz equation (O2), to estimate the Minimum Detection Time (MDT), defined as the time to attain 3% of CO2 (MDT1) or a decrease of the content of O2 by 3% (MDT2). Then, MDT1 and MDT2 were submitted to a linear regression procedure, using cell concentration as independent variable; the correlations "MDT1/cell concentration" and "MDT2/cell concentration" showed high determination coefficients (>0.983). Moreover, the regression procedure pointed out that both MDT1 and MDT2 decreased by ca. 3 h for an increase of cell count of 1 log cfu mL-1. Preliminary validation in milk pointed out that the error associated with the regression line "MDT2/cell concentration" was below 5%.