The recent discovery1,2 of superconductivity in the three-dimensional perovskite system (Ba, K)BiO3 has added a new group of compounds to the family of high-transition-temperature (high-Tc) superconductors. (Ba, K)BiO3 contains a three-dimensional BiO network rather than the CuO planes found in two-dimensional high-Tc systems such as YBa2Cu3O7, (La1.85Sr0.15)CuO4, Bi–Ca–Sr–Cu–O and Tl–Ba–Ca–Cu–O. There are, however, a few key features shared by (Ba, K)BiO3 and the two-dimensional systems; for example the parent compounds BaBiO3 and La2CuO4 both have one valence electron per Bi (or Cu) and doping by K (or Sr) introduces holes into the system as charge carriers. To explore the possible effects of magnetism in the (Ba, K)BiO3 system and its related compounds, we have performed muon spin rotation (μSR) experiments on BaBiO3, (Ba, K)BiO3 and Ba(Bi0.9Pb0.1)O3, the latter being a member of another oxide superconductor system, Ba(Pb, Bi)O3 (ref. 3), to search for static magnetic order. In the present study, no signature of magnetic order was found in any of the above systems above T = 10 K. This is in sharp contrast to the two-dimensional systems, where static magnetic order appears in the vicinity of superconductivity.