The authors introduced a technique for assessment of cells with micronuclei in stimulated human peripheral lymphocytes using cytochalasin B (CB technique). The spontaneous level of cells with micronuclei was assessed in an ageing population group. The group comprised fifteen subjects (12 women and 3 men), mean age 79.7 +/- 6.7 years. The spontaneous level of cells with micronuclei was 33.7 per 1000 evaluated cells, i.e. 3.37%. The authors consider the possibility of introducing the test for assessment of micronuclei in human peripheral lymphocytes using cytochalasin B as an alternative test in the cytogenetic analysis of chromosomal aberrations in human peripheral lymphocytes.