We have used the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope to obtain V and I images of seven nearby galaxies .
For each , we have measured a distance using the tip of the red giant branch ( TRGB ) method .
By comparing the TRGB distances to published Cepheid distances , we investigate the metallicity dependence of the Cepheid period-luminosity relation .
Our sample is supplemented by 10 additional galaxies for which both TRGB and Cepheid distances are available in the literature , thus providing a uniform coverage in Cepheid abundances between 1/20 and 2 ( O/H ) _ { \odot } .
We find that the difference between Cepheid and TRGB distances decreases monotonically with increasing Cepheid abundance , consistent with a mean metallicity dependence of the Cepheid distance moduli of { { \delta { ( m - M ) } } / { \delta [ O / H ] } } = { -0.24 \pm 0.05 } mag dex ^ { -1 } .