Superconductivity in UPt3

The theory of basal plane anisotropy of upper critical field in hexagonal heavy fermionic superconductors UPt3 is developed. It is shown, that the recent experimental discovery of the sign change of this anisotropy above the tetracritical point in (H, T) plane proves to be the most important experimental argument in favour of the model of unconventional superconductivity mixing in the order parameters transforming according to different one-dimensional representation of the hexagonal group. The current model describing the superconducting phase transition splittig in UPt3 are critically overviewed in the light of mentioned observation. (orig.)