We estimated silicate uptake kinetics for 8 spring diatom species using a model based on time series measurements of the depletion of dissolved silicate (DSi) and increases in biomass. Furthermore, the carbon: nitrogen: silicate stoichiometric relationships and maximum growth rates were determined. Differences in DSi uptake kinetics and maximum growth rate were distinct among the species. All the most common diatom species (Chaetoceros wighamii, Pauliella taeniata, Skeletonema costatum and Thalassiosira baltica) were relatively lightly silicified and had variable but relatively low half-saturation constants (Ks), indicating that they are well adapted to low DSi concentrations. The less common Diatoma tenuis and Nitzschia frigida had higher Ks values, suggesting that they are more vulnerable to DSi limitation. The much used nitrogen:silicate ratio of 1 for marine diatom biomass was too low for most of the examined species, while a ratio of 2-3 seems to be more appropriate for these Baltic Sea species.