Use of probiotic-containing foods and probiotic supplements is increasing; however, few studies document safety and tolerability in conjunction with defined clinical end points. This paper reports the effects of 150 days of supplementation with either a single- (Bifidobacterium animalis subsp. lactis Bl-04) or a double-strain (Lactobacillus acidophilus NCFM and Bifidobacterium animalis subsp. lactis Bi-07) probiotic on routine haematology and clinical chemistry measures in healthy active adults. Pre- to post-intervention changes in laboratory measures were determined and compared between supplement and placebo groups. Overall there were few differences in routine haematology and clinical chemistry measures between supplement and placebo groups post-intervention. Exceptions included plasma calcium (P=0.03) and urea (P=0.015); however, observed changes were small and within assay-specific laboratory reference ranges. These data provide evidence supporting the use of these probiotic supplements over a period of 5 months in healthy active adults without obvious safety or tolerability issues.