  Massive BA-type supergiants are among the visually brightest stars in
galaxies with active star formation. As such they are versatile tools for
studies of stellar and galactochemical evolution. Moreover, they can act as
distance indicators for the calibration of the cosmological distance scale. In
the present work abundance patterns of the light elements helium, carbon,
nitrogen and oxygen are investigated in several Galactic BA-type supergiants in
the mass range between 8 and 18 M_sun. Based on high-resolution and high-S/N
Echelle spectra obtained with FOCES on the Calar Alto 2.2m telescope, model
atmosphere analyses are performed using state-of-the-art non-LTE spectrum
synthesis. Stellar parameters and chemical abundances are determined with high
accuracy. This gives tight observational constraints on the evolutionary status
of the stars. Objects evolving from the main sequence to the red supergiant
stage and those on a blue loop can be distinguished by their mixing signature
(pure rotational vs. first dredge-up). The most sensitive tracer of nuclear
processed matter, the N/C ratio, indicates a higher mixing efficiency than
predicted by current evolution models of rotating stars with mass-loss.
