infectivity titre of IBR virus in MDBK cells using monolayels suspension and roller system revealed that the roller system produced the highest infectivity titre with an increase of log 1.0 than their corresponding monolayer cell culture. On the 
other hand, the infectivity titres in cell suspension cultures were log 10 0-6-log 10 0.8 lower than their corresponding monolayer cell culture system. influence of DEAE-dextran for the enhancement of IBR virus infectivity in different cell culture systems, 25 ug DEAE-dextran per ml is considered the safest concentration to theMDBK and VERO cell lines and giving these resulls: 
l- Infectivity titre of IBR virus was markedly increased under the effect of both serial passages and DEAE-dextran in MDBK and VERO cells which showed an increase of log10 1.2 and logyg 1.0, respectively more than their respective non treated passages.
2- In th roller system, DEAE-dextran enhanced the growth of virus by about 0.9, 0.7 logio more than growth of untreated virus in both MDBK and VERO cell lines, respectively.
 3- The highest titre obtaincd when using DEAE-dextran MDBK roller system was logio 9.2 TCIDso/ml.