Abstract 

  The rate of star formation is proportional to the mass of molecular gas over a broad range of objects...but not all. The mass of dense gas, more difficult to measure, appears to a better indicator of the star formation rate. The HCN(1-0)line luminosity is the standard, and possibly the best, tracer of the dense gas mass. However, while we expect the tight relationship between dense gas and star formation to hold regardless of metallicity, the HCN emission becomes very weak in low metallicity systems. I will present recent and still unpublished observations of dense gas observations in low metallicity local galaxies covering a variety of emission lines. And discuss the possible reasons for the weak HCN emission and how this could affect measurements of high redshift systems.