Received April 30, 2002
Accepted May 12, 2002

This work was performed with Mus domesticus domesticus embryos and cons istecl or two experiments. The objective of the experiment I was to evaluate the toxicity of the cryoprotectors agents on embryo development. The experiment II was designed to determine the hatched blastocyst rate after vitrification using two different procedures to loading the embryos into the straws. The data of the experiments were analyzede by Qui-square Test with 5% of significance. When the test showed a significative difference among the treatments, the residues analyses were calculated. Based on these results it is concluded that the brief straw loading exposure of Mus domesticus domesticus expanded blastocysts to 9.0M of EG+6%BSA in PBS solution, with previous equilibration in 1.8M EG+6%BSA in PBS solution was not harmful to embryo development in vitro. The use or 0.12ml vitrification straws gave significantly higher hatched blastocyst rate of Mus domesticus domesticus. The presence of mineral oil in the vitrification straw, independent of the volume used, was harmful to the development in vitro of embryos of Mus domesticus domesticus expanded blastocysts.