A \'new\' generation of synthetic antirhinovirus compounds has recently become available for in vitro evaluation. Thus a new group of compounds from Janssen was found to be 10-fold more active than enviroxime or 57-fold more active than dichloroflavan (DCF), against human rhinovirus 9 (HRV-9). In addition, they were also some 5- and 10-fold more potent than enviroxime and DCF, respectively, against HRV-2. Similarly, a \'new\' series of antirhinovirus compounds from Roche, although as active as enviroxime against HRV-9, were found to be 4-fold more potent than DCF against the same virus. Moreover, they were 45- and 90-fold more active than enviroxime and DCF, respectively, when tested against HRV-2. We found that generally HRV-2 was more sensitive to these new compounds than HRV-9. In this study we also report on the synergistic interaction between these new synthetic substances and also with some of the earlier compounds such as DCF and enviroxime and we discuss the possible implication of this synergistic activity regarding the future prevention and treatment of common colds caused by rhinoviruses.