Similarities between a unicellular eukaryotic organism Tetrahymena and human cells as well as the ease in management of Tetrahymena cultures stimulated us to investigate this organism as a model for a rapid in vitro test for drugs from the NSAIDs family that could allow for a cellular assay to predict drug blood therapeutic levels. For this purpose, we quantified, by image analysis, changes in Tetrahymena thermophila (TT) cell area as a function of NSAID concentration, and found a correlation with drug effective plasma levels in humans.