1  Abstract Our experiment was done to find out the rate of photoreactivation on the haploid cells. The name of the yeast stain we used was HA1. We used five plates, one of them was the haploid control. Two of the five plates, with their lids off, were exposed to ultraviolet B for twenty seconds each at a time, and were kept in the dark after exposure. The other two plates were exposed to ultra violet B for twenty seconds with their lids off. Then they were exposed to visible light(300 watt halogen light) for seven minutes sat one foot with their lids on. All five YED agar plates were kept in the incubatora at a temperature of thirty seven degrees celcius for one day and three days at room temperature out of the incubator. After counting the haploid colonies we got twenty colonies in the haploid control plate, eleven and twenty four colonies in the two ultraviolet exposed plates, and seven and fourteen in the plates where photoreactivation was done.NP HJwoA`7eD@`Me'D  @gT` ^8^0gpg:o|`hH4  hhrhho`  o`,NP HJ@B79uwJ   0Roman 10cpikround Information Photoreactivation is one of the most effective repair systems for ultraviolet radiatio