Radiative lifetimes of nine of the levels np 'P:/,, np 'D:,,. s,z andnp 'D:/, in the homologous ions Ar I1 (n = 4), Kr I1 (n = 5 ) and Xe I1 (n = 6) have been measured with the beam-laser method. The measured lifetimes are compared with lifetime values from other experimental and theoretical works and a thorough discussion of the discrepancies between the results obtained with different techniques is made. Older measurements of transition probabilities are put on an accurate scale using the new lifetime values. The f-values of some strong transitions from levels in the np configuration in Ar 11, Kr I1 and Xe I1 are compared and are found to be approximately equal.