  NGC 6388 and NGC 6441 are anomalies among Galactic globular clusters in that
they cannot be readily place into either Oosterhoff group I or Oosterhoff group
II despite their significant numbers of RR Lyrae variables. The mean pulsation
periods, <Pab>, of their RRab variables, at 0.71 d and 0.76 d, respectively,
are even larger than for Oosterhoff II clusters. Moreover, Oosterhoff II
clusters are very metal-poor, whereas NGC 6388 and NGC 6441 are the most
metal-rich globular clusters known to contain RR Lyrae stars. The location of
the NGC 6388 and NGC 6441 RRab variables in the period-amplitude diagram
implies that the RR Lyrae stars in those two clusters are brighter than
expected for their metallicities. Our results therefore indicate that a
universal relationship may not exist between the luminosity and the metallicity
of RR Lyrae variables.
