The dominant lethal assay was utilized to assess the reproductive performance in male mice, possible genetic hazards, and persistent damage of aluminum (Al). Al chloride, AlCl(3), was administered subcutaneously to CD-1 adult male mice at dosages of 0, 7, or 13mg Al/kg body weight/day for 2 weeks of pre-mating periods. Females were not dosed at any time during this study. At the end of the exposure period, each male was caged with three virgin females each day. The mean mating frequencies of the Al-treated groups reduced consistently from week 4 to 6, and a dramatic reduction in male fertility was also observed. However, the mating frequency restored to near normal control levels as the experiment terminated. Results showed significantly higher numbers of post-implantation losses, foetal mortality, and induced petechial haemorrhage; also significant decreases in body weights of viable foetus throughout weeks 3-8 in the Al-treated groups. The weights of the reproductive organs of the Al-dosed animals decreased significantly as Al accumulation increased in the testes. The spermatogenetic impairment within the seminiferous tubules was also apparent. Nevertheless, these disturbances disappeared at the end of the experiments. In summary, the results demonstrated that Al exerted substantial hazards on male reproductive function and produced genetic toxicity. However, these effects were found to be reversible.