We report the development and validation of a qPCR based method for estimation of the toxic benthic dinoflagellate Ostreopsis cf. ovata in the complex matrix of marine aerosol at Sant Andreu de Llavaneres beach (northwestern Mediterranean Sea). Toxic events in humans after inhalation or cutaneous contact have been reported during O. cf. ovata blooms and were attributed to palytoxin (PLTX)-like compounds produced by this microalga. Similar PCR efficiencies of plasmid and cellular environmental standard curves (98 and 100%, respectively) allowed obtaining the rDNA copy number per cell. The analytical sensitivity was set at 2 × 10(0) rDNA copy number and 8 × 10(-4) cell per reaction. Based on spiking experiments, we evaluated the aerosol filter inhibitory activity and recovery rate of cells from filters, then normalized the abundance data of toxic O. cf. ovata. The abundance in marine aerosol during the bloom varied in the range of 1-102 cells per filter. Analytical determinations were also applied to detect palytoxin in field samples. No palytoxin was detected in the aerosol filters, and the estimation of PLTX like-compound concentrations in microepiphytic assemblages varied between 0.1 and 1.2 pg/cell.