  We use the analysis of the heavy element abundances (C, N, O, S) in
circumstellar nebulae around Luminous Blue Variables to infer the evolutionary
phase in which the material has been ejected.
  (1) We discuss the different effects that may have changed the gas
composition of the nebula since it was ejected
  (2) We calculate the expected abundance changes at the stellar surface due to
envelope convection in the red supergiant phase. If the observed LBV nebulae
are ejected during the RSG phase, the abundances of the LBV nebulae require a
significantly smaller amount of mass to be lost than assumed in evolutionary
models.
  (3) We calculate the changes in the surface composition during the main
sequence phase by rotation induced mixing. If the nebulae are ejected at the
end of the MS-phase, the abundances in LBV nebulae are compatible with mixing
times between 5 x 10^6 and 1 x 10^7 years. The existence of ON stars supports
this scenario.
  (4) The predicted He/H ratio in the nebulae are significantly smaller than
the current observed photospheric values of their central stars.
  Combining various arguments we show that the LBV nebulae are ejected during
the blue SG phase and that the stars have not gone through a RSG phase. The
chemical enhancements are due to rotation induced mixing, and the ejection is
possibly triggered by near-critical rotation. During the ejection, the outflow
was optically thick, which resulted in a large effective radius and a low
effective temperature. This also explains the observed properties of LBV dust.
