The effects of oral administration of a lactococcal strain on physiological changes associated with ageing were investigated using senescence-accelerated mice (SAM). SAM develop normally, but then show an early onset and irreversible advancement of senescence. SAMP6 is a SAM strain that develops osteoporosis with ageing. Oral administration of heat-killed Lactococcus lactis subsp. cremoris H61 (strain H61) to aged SAMP6 mice was associated with reduced bone density loss, a suppression of incidence of skin ulcers and reduced hair loss, compared with controls. Spleen cells from mice fed strain H61 produced more interferon-γ and IL-12 than those from control mice, suggesting that administration of strain H61 altered immune responses. The numbers of viable cells of Bifidobacterium sp., Bacteroides sp. and Enterococcus sp. in faeces were similar for mice fed the strain H61 and control diets, but counts for Staphylococcus sp. were significantly lower (P < 0·05) in mice fed strain H61. Mice fed strain H61 had similar serum concentrations of thiobarbituric acid-reactive substances as in controls, indicating a lack of effect on lipid peroxidation status. Administration of living cells of strain H61 or fermented milk containing strain H61 was also associated with a suppression of incidence of skin ulcers and reduced hair loss. These results indicate that oral administration of strain H61 has the potential to suppress some of the manifestations associated with ageing.