Sex determination in genomic DNA from human blood leucocytes was performed by amplification of human Y chromosome-specific DNA sequences using PCR technique. A clear DNA fragment(154 nucleotides long) was appeared only in the male genomic DNA, but no specific band was observed in the case of female genomic DNA and negative control. To know the sensitivity of this method, the amplification reaction was performed in genomic DNA diluted to 2pg equivalent to the amonut present in the single human cell, and clear band also observed. The PCR amplification was so succesfully performed in the single leucocyte separated from human blood using micromanipulator that this techniqe is assumed to be applied to single blstomere before embryo transfer.