The MBX gene is a novel paired-type homeobox gene. It plays a number of critical roles in the development of the eyes in the zebrafish. The knockdown of the mbx expression by morpholino antisense oligonucleotides leads to a reduction in the size of eyes and tectum in the zebrafish. We investigated whether the human MBX gene was associated with susceptibility to microphthalmia by analyzing four Korean families demonstrating microphthalmia with congenital cataract. Mutational analysis was performed on the human MBX gene using these families. However, no mutations could be detected. Therefore, no indications were found for an association between the MBX gene and microphthalmia with congenital cataract in humans.