  The mass-loss rates and dust-to-gas ratios of obscured Asymptotic Giant
Branch (AGB) stars are investigated for samples with different initial
metallicities: in the Small and Large Magellanic Clouds (SMC & LMC) and in the
Milky Way. The properties of their circumstellar envelopes can be explained in
a consistent way if, both for obscured M-type AGB stars and for obscured carbon
stars, the total (gas+dust) mass-loss rate depends only weakly on initial
metallicity whilst the dust-to-gas ratio depends approximately linearly on
initial metallicity.
