Effects of baicalein and biochanin A on H5N1 titres in combination with N-acetyl-L-cysteine (NAC). A549 cells were infected with H5N1 strain A/Thailand/1(Kan-1)/04 (MOI 0.01). Drugs were continuously present starting with a 1 h pre-incubation period. Virus titres were determined 48 h post infection. A) Effects of NAC on H5N1 replication, *P < 0.05 relative to virus control; B) Effects of NAC on H5N1 titres in the presence of the flavonoids baicalein 40 μM or biochanin A 40 μM, *P < 0.05 relative to flavonoid alone. Values are presented as mean ± S.D. from three different independent experiments.