The calluses were indeced from turnips, Brassicae campestris L. which were susceptible and resistant to Plasmodiophora brassicae in Murashige-Skoog’s agar medium supplemented with 1.0 ppm 6-benzylaminopurine and 0.5 ppm α-naphthalene acetic acid. When a 10 μl water suspension containing 10⁴ resting spores of P. brassicae was placed on the surface of the calluses, about 3 × 10⁵ zoosporangium-like spheroids (SLS) were recovered from the susceptible calluses after 24 h of the treatment but no SLS was found in the resistant callus. On 6th day after the treatment, the SLS increased to about 4 × 10⁶ in the susceptible callus. Upon inoculation of resistant callus with 10⁴ resting spores, the phenylalanine ammonia lyase (PAL) activity increased about 4-fold after 20 h, however, such increase was not observed in the susceptible callus during the same period. The consitutive PAL activity of susceptible callus was roughly one 6th of that of resistant callus.