COMMENTARY fected cells τ was estimated from the ‘shoulder’of the virusconcentration decay curves to be about 1.25 days5. Our interpretation differs fundamentally from that accepted at present. We explain the kinetics entirely in terms of changes in numbers of cells infected after the introduction of drugs, not before. Although current models allow for incomplete blocking of viral transmission, this is usually accommodated only as a small correction to exponential cell death kinetics (Appendix 2). There is a fundamental difference in the way these divergent interpretations are extended to phase II.