SummaryThe microflora of ten batches of La Serena cheese, made from raw milk of Merino ewes and using vegetable rennet as coagulant, was monitored throughout a 60 d ripening period. After 15 d, lactic acid bacteria predominated in the interior of the cheese, whilst lactic acid bacteria and lactic acid-utilizing species of yeasts and moulds predominated on the cheese surface. Coagulase-positive staphylococci were not detected in the interior or on the surface of any of the cheeses after 45 d and faecal coliforms were not found after 60 d. Higher death rates of staphylococci and coliforms were recorded for cheese made in spring than for the cheese made in winter.