Objective:To check the effects of the vaccines on the hematopoietic system and weight of mice after immunization.Methods:The study was done with the Expanded Programme on Immunization vaccines donated by the Ministries of Health of Abia and Imo States of Nigeria.The vaccines were collected from the cold-chain stores and transported in vaccine carriers to the cold-chain facility in Nnamdi Azikiwe University Teaching Hospital within 3 hours of collection.They were used to immunize a total of 160 mice.The Ethics Committee of Nnamdi Azikiwe University Teaching Hospital,Nnewi of Anambra State,Nigeria approved the protocol.Results:Mice body weight changes test showed that the mice all had increased body weight at Days 3 and 7 post-immunization and none died during the 7 d post-immunization observation.The percentage weight gains of the mice compared with the control were 69%.70%,64%.63%,65%and 68%for oral polio vaccine,diphtheria-pertussis-tetanus.bacillus CalmetteGuerin,measles,yellow fever and hepatitis B vaccines respectively collected from Imo State.The mice immunized with oral polio vaccine,pentavalent.bacillus Calmette-Guerin.measles,yellow fever and hepatitis B vaccines collected from Abia State had 123%.114%,121%.116%,142%and 119%weight gain respectively compared with the control.Leukocytosis promoting toxicity test showed that none of the vaccines was able to induce proliferation of leukocytes up to ten folds.Leukopenic toxicity test showed that all the vaccines had an leukopenic toxicity test value higher than 80%of the control(physiological saline).Conclusions:The vaccine samples tested were safe and did not affect the hematopoietic system adversely.The storage conditions of the vaccines in the States’ cold-chain stores had not compromised the safety of the vaccines. Objective: To check the effects of the vaccines on the hematopoietic system and weight of mice after immunization. Methods: The study was done with the Expanded Program on Immunization vaccines donated by the Ministries of Health of Abia and Imo States of Nigeria. The vaccines were collected from the cold-chain stores and transported in vaccine carriers to the cold-chain facility in Nnamdi Azikiwe University Teaching Hospital within 3 hours of collection. They were used to immunize a total of 160 mice. The Ethics Committee of Nnamdi Azikiwe University Teaching Hospital , Nnewi of Anambra State, Nigeria approved the protocol. Results: Mice body weight changes test showed that the mice all had increased body weight at Days 3 and 7 post-immunization and none died during the 7 d post-immunization observations. Percentage weight. gains of the mice compared with the control were 69% .70%, 64% .63%, 65% and 68% for oral polio vaccine, diphtheria-pertussis-tetanus.bacillus CalmetteGuerin, measles, yellow fever and hepatitis B vaccines individually collected from Imo State. The mice immunized with oral polio vaccine, pentavalent. bacillus Calmette-Guerin. measles, yellow fever and hepatitis B vaccines collected from Abia State had 123% .114%, 121% .116% 142% and 119% weight gain respectively compared with the control. Leukocytosis promoting toxicity test showed that none of the vaccines was able to induce proliferation of leukocytes up to ten folds. Leukopenic toxicity test showed that all the vaccines had an leukopenic toxicity test value higher than 80% of the control (physiological saline) .Conclusions: The vaccine samples tested were safe and did not affect the hematopoietic system adversely. the storage conditions of the vaccines in the States’ cold-chain stores had not compromised the safety of the vaccines .