Four different diatom species (Chaetoceros debilis, Chaetoceros didymum, Cylindrotheca fusiformis, Nitzschia angularis) were studied by solid-state ²⁹Si MAS NMR spectroscopy. To determine the Q²:Q ³:Q⁴ ratios in the biosilica deposits of the diatoms, quantitative ²⁹Si MAS NMR experiments were performed. This analysis did not reveal any differences regarding the molecular architecture of the silica (i.e. the degree of condensation of the SiOH units (2 ≡SiOH → ≡Si-O-Si≡ + H₂O)) from the different diatom species. However, complete cells showed significantly smaller Q⁴:Q ³ ratios (1.8-1.9) than extracted cell walls (2.5-2.8), indicating the existence of intracellular pools of less condensed silica.