Effect of binarity on the local stellar mass density

Summary Considering the existence of many unresolved binary systems among the stars used to derive the stellar luminosity function, we have estimated the increase in the total mass density in the solar neighbourhood. Such an increase depends on the fraction of stars which are unresolved binaries, but conservative estimates give a value larger than 0.004M _⊙ pc⁻³. Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983.