However, it was more difficult to eliminate Agro- bacterium after longer periods of co-cultivation. Cer vera et al. (1998) reported that the 5-day culture period resulted in overgrowth of Agrobacterium and a subsequent decrease in the frequency of transformed shoots, although 5-day co-cultivation was the most effective for increasing the frequency of transient GUS expression in citrange explants. Therefore, the period of co-cultivation should be optimized. We investigated the effect of varying the periods of co-cultivation with transient expression of the uid A gene. Co-cultivation for 3 days showed much higher GUS expression compared with 1- or 2-day co-cultivations(Fig. 1). However, transient GUS exprssion did not vary significantly over 3- to 6-day co-cultivation. Agro bacterium could be substantially eliminated from the co-culture medium of the 3-day co-cultivation in garlic calluses. Thus, we used a 3-day co-cultivation rou tinely