The anomalous temperature dependence of the in-plane H-c2 anisotropy of Sr2
RuO4 is discussed based on a model which includes spin-orbit coupling effec
ts. While the basic superconducting state corresponds to a chiral p-wave sl
ate, the in-plane magnetic field generates a nonunitary state which leads t
o the observed anomalous anisotropy. Although this effect is connected with
spin-orbit coupling and multi-band effects, it does not affect anisotropy
parameters which determine the vortex lattice structure in the mixed state
for fields parallel to the c-axis. In this manner the discrepancy between l
ow-temperature in-plane anisotropy and c-axis vortex lattice orientation is
resolved.