The global budget and hemispheric distribution of methyl chloroform (CH3CCl3) have been used to determine the average residence times of CH3CCl3, and HO radical concentrations, in the two hemispheres. It is concluded that a global average residence time (&tgr;a) of about 8 years best fits the observational data. It is further shown that the residence time of CH3CCl3 in the northern hemisphere (&tgr;n) is probably significantly longer than in the southern hemisphere (&tgr;s). While the ratio of &tgr;n/&tgr;s is quite sensitive to interhemispheric exchange rates (&tgr;e) and the north/south concentration gradients of CH3CCl3, a strong case for &tgr;n>1.6&tgr;s[(HŌ)S.H.>1.6(HŌ)N.H.> can nevertheless be made. Best estimates suggest that the global average HO concentration [{ (HO)N.H.+(HŌ)S.H.}/2> of 4.1¿105 HO/ml is most compatible with the observed data. The distribution of HO in the two hemispheres is, however, found to be asymmetric with southern hemispheric HO concentrations 1.6 to 3 times higher than the northern hemispheric values. It is inferred that this HO gradient is caused by atmospheric carbon monoxide, which is a principal sink for HO. The implications of these hemispheric HO asymmetries and the uncertainties involved are discussed.