CYP1A2 and hydrops fetalis: Although CYP1A2 is the main enzyme responsible for the conversion of FLU to HF in both rat and humans (Shet et al., 1997; Chang et al., 2000), the rat liver microsomal (RLM) incubation derived in vitro Vmax of FLU hydroxylation to HF amounting to 0.063 ± 0.008 nmol/min/mg protein (Chang et al., 2000) appears to be 4-fold lower than the HLM derived and optimized in vitro Vmax for FLU hydroxylation to HF of 0.27 nmol/min/mg protein obtained in this work.