The survival of four strains of yeast belonging to the species Saccharomyces cerevisiae, Candida wickerhamii, Candida boidinii and Williopsis californica was studied in extra virgin olive oil flavoured with garlic, lemon, oregano and red chilli pepper. The ingredients used in the doses of 1%, 5% and 10% profoundly modified the habitat of the extra virgin olive oil, reducing drastically, in 90 days of storage, the survival of the yeasts by 20-50%, in the following decreasing order: lemon, garlic, oregano and red chilli pepper. Among the yeasts studied, W. californica strain 1639 was found to be one of the most sensitive, while S. cerevisiae strain 1525 was one of the most tolerant regarding the ingredients present in the flavoured olive oil. The observations carried out with a scanning electron microscope (SEM) highlighted the presence of frequent lesions on the cellular wall of C. wickerhamii 1532, C. boidinii 1638 and S. cerevisiae 1525 and only in a few rare cases in W. californica 1639. Nevertheless, since the survival of W. californica 1639 in the flavoured olive oil was compromised to a greater extent in respect to the other species, it is plausible to deduct that the damage to the cellular wall represents only one of the causes responsible for the death of the yeasts in the flavoured olive oil.