We collected a sample of 100 galaxies for which different observers have determined colour indices of globular cluster candidates .
The sample includes representatives of galaxies of various morphological types and different luminosities .
Colour indices ( in most cases ( V - I ) , but also ( B - I ) and ( C - T _ { 1 } ) ) were transformed into metallicities [ Fe / H ] according to a relation by Kissler-Patig ( 1998 ) .
These data were analysed with the KMM software in order to estimate similarity of the distribution with uni- or bimodal Gaussian distribution .
We found that 45 of 100 systems have bimodal metallicity distributions .
Mean metallicity of the metal-poor component for these galaxies is { \langle [ Fe / H ] \rangle } = -1.40 \pm 0.02 , of the metal-rich component { \langle [ Fe / H ] \rangle } = -0.69 \pm 0.03 .
Dispersions of the distributions are 0.15 and 0.18 , respectively .
Distribution of unimodal metallicities is rather wide .
These data will be analysed in a subsequent paper in order to find correlations with parameters of galaxies and galactic environment .