At the light of the increasing evidence that malignant transformation is a multistep process the wide correlation between growth in soft agar and various degrees of tumorigenicity suggests that this could be a property of the early stages of malignant transformation. In the present paper we give evidence indicating that colony formation in agarose gels containing deoxyglucose can operate as a more restrictive criterium than growth in soft agar for malignant transformation in vitro, possibly associated to advanced stages in this process.