This study was conducted to investigate the efficacy of the Newcastle disease (ND) live vaccines from different commercial sources used in different programs for vaccination of chicks having maternal antibodies against Mycoplasma infection. The immune response was estimated using HI and challenge tests. The effect on the chicken performance was estimated by the detection of the body weight gain. The role of vaccines in stimulating respiratory bacterial stress was pointed out by the lesion scores. Birds vaccinated with live vaccines from source (2) showed higher HI titers than those vaccinated with vaccine from source (1) and birds received the 2nd vaccination from heterologous source showed lower titers than those received from homologous source. Results of the challenge test indicated that birds vaccinated with live ND vaccines from one source and those vaccinated with Hitchner B1 at 33-days of age instead of La Sota showed 100% protection rate as compared with 95 % followed by vaccination with heterologous La Sota. Birds
received Hitchner B1 of vaccine source (1) showed only 85% protection rate. All vaccinated chicken groups showed feed conversion rates lower than the non-vaccinated control one. Groups received Hitchner B1 as a 3rd dose of the vaccine showed higher rates than those vaccinated with La Sota. 
Results of the lesion score for chronic respiratory disease (CRD) in vaccinated groups with different regimes revealed that birds received ND vaccinal strains from source (1) having higher scores than those received ND vaccines from the 2nd source. Administration of Hitchner B1 vaccine at 33-days of age showed lower scores. Hitchner B1 can be recommended in vaccination of chickens derived from Mycoplasma infected hens.