Poly(1,1'-ferrocenyldimethylsilane)-b-poly(methyl methacrylate) (PFS-b-PMMA) diblock copolymers were blended with the corresponding homopolymers, PFS and PMMA. The obtained blends were investigated with respect to their microphase morphologies in the bulk. Special attention was paid to those compositions which are close to the transition from the cylindrical to the lamellar regime, i.e., where the overall PFS volume fractions in the blends were around phi(PFS) approximate to 0.40. This is because there the bicontinuous gyroidic morphology should arise. However, in samples prepared from high-molecular-weight diblock copolymers (M-n greater than or equal to 40 000 g/mol) and PFS homopolymers a direct transition of the cylindrical into the lamellar phase was found with increasing PFS content. Such a direct transition of two classic morphologies was also observed in blends of low-molecular-weight diblock copolymers (M-n approximate to 27 000 g/mol) and PMMA homopolymers where the PIPS volume fraction was around phi(PFS) approximate to 0.40-provided the annealing temperature was rather low (165 degreesC). The same samples, on the other hand, show the formation of a gyroidic phase when the annealing temperature was raised to 190 or 220 degreesC. This result can be explained by the lower segregation tendency of the two constituents at higher temperatures, expressed by a lower Flory-Huggins interaction parameter chi.