Abstract
By means of radio continuum observations of 29 stars with spectral types O8-B3 we searched for evidence of the existence of a bi-stability jump in stellar mass loss around T_{eff} ≈ 21 kK. Although there are quantitative discrepancies, the qualitative behaviour of the wind efficiency with effective temperature appears to be in line with theoretical predictions. Observations of new cases are fundamental to confirm these results.
