In somatic cells of the rodent Eliomys quercinus (dormouse) nucleoli are found on chromosomes 14 and 22. Variation in silver stainability of nucleolar organizing regions at metaphase was concluded to reflect variation in nucleolar activity in the preceding interphase. It could be demonstrated that variation in nucleolar organizing region stainability was not independent for the two homologues of the same chromosome, nor for different chromosomes, but the interactions were complex. This is suggested to reflect a mechanism of regulation of nucleolar activity. The interactions between nucleolar organizing regions varied among individuals.Key words: Eliomys quercinus, nucleolar organizing regions, nucleolar organizing region activation.