The study was carried out to determine the effectiveness and safety of the infrared 1.48 microm laser in cleavage stage mouse embryo biopsy, compared to the conventional acid Tyrode's solution. One hundred and thirty cryopreserved cleavage stage mouse embryos were included in the study. Fifty embryos were biopsied by acid Tyrode's solution. Forty-seven embryos were biopsied by the infrared 1.48 microm laser. Thirty-three embryos were incubated without biopsy as the control group. Thirteen of 50 embryos in the acid Tyrode's group and 16 of 47 in the laser assisted group became cavitating morulae on day 4, meanwhile 23 of 33 in the control group reached this stage. The blastocyst formation of acid Tyrode's, laser assisted and control group were 94.0, 97.8 and 100.0 per cent, respectively. The hatching rate of acid Tyrode's solution, laser assisted and control group were 78.7, 84.7 and 63.6 per cent, respectively. No significant difference in blastocyst formation and hatching rate was found. The percentage of grade I blastocysts in control group (96.9%) was significantly higher than those in acid Tyrode's solution (68.0%) and the laser assisted group (76.0%). There was no significant difference in the percentage of grade 1 blastocysts between the acid Tyrode's solution and the laser assisted group. In conclusion, the infrared 1.48 microm wavelength laser may be an alternative to acid Tyrode's solution in embryo biopsy.