Cendrat del Montsec is an on-farm manufactured cheese made with raw milk, indigenous lactic culture and animal rennet, and is consumed after ripening for 60 days at 10-15°C and 90-95% relative humidity (rh). The microflora of eight batches were monitored throughout 9 weeks of ripening, and the interior and surface of cheeses were analyzed. ANOVA performed on the log transformation of microbial counts showed that the batch had a significant effect on levels of all microbial groups considered but that no effect in any microbial group in the interior of cheeses was observed for samples from the same batch. High total counts throughout ripening with slight decreases were observed. Lactic flora predominated in the interior and the most notable of them were those cultured in MRS agar; comparatively, lactic flora in M17 agar were only higher in the curd and its later decrease was more noticeable. Leuconostoc was the most stable flora during ripening, being the only one whose counts were not affected by the age of the cheese. Slight decreases were also observed for yeast and molds. Psychrotrophic micro-organisms increased during coagulation, showing the highest counts in the curd, and decreased until 6 weeks. Significant reductions of potentially pathogenic flora were observed. Enterobacteria decreased throughout the ripening period as well as faecal coliforms, which were never detected after 9 weeks. Counts of total coliforms fell during the first 3 weeks, followed by a stabilization. Higher counts for winter batches compared to those of spring were found for counts of psychrotrophic microorganisms, enterobacteria and coliforms (total and faecal). During coagulation, coagulase-positive Staphylococcus increased and a high dispersion of counts in final cheeses were achieved. Total surface flora were high throughout the ripening. Surface mycoflora was the only population where significant differences between units of the same batch were found. © 1994 Academic Press Limited.