The fluorophore [2-(4-pyridyl)-5{[4-dimethylaminoethyl-aminocarbamoyl-methoxy]phenyl}oxazole], in short PDMPO, is incorporated in newly polymerized silica in diatom frustules and thereby provides a tool to estimate Si uptake, study diatom cell cycles but also determine mortality-independent abundance-based species specific-growth rates in cultures and natural assemblages. In this study, the theoretical framework and applicability of the PDMPO staining technique to estimate diatom species specific-growth rates were investigated. Three common polar diatom species, Pseudo-nitzschia subcurvata, Chaetoceros simplex, and Thalassiosira sp., chosen in order to cover a broad range of species specific frustule and life-cycle characteristics, were incubated over 24 h in control (no PDMPO) and with 0.125 and 0.6 μM PDMPO addition, respectively. Results indicate that specific-growth rates of the species tested were not affected in both treatments with PDMPO addition. The specific-growth rate estimates based on the PDMPO staining patterns (μPDMPO) were comparable and more robust than growth rates estimated from the changes in cell concentrations (μcc). This technique also allowed to investigate and highlight the importance of the illumination cycle (light and dark phases) on cell division in diatoms.