Polyclonal antisera were raised to whole and sonicated fractions of resting spores of Plasmodiophora brassicae, the causal agent of clubroot disease. Cross reactivity of antisera was assessed against a wide range of soil-borne pathogens. Antiserum raised to whole resting spores was used to probe artificially infested soils by indirect immunofluorescence. Resting spores could be detected at a concentration as low as to 1 × 102 spores per g in artificially infested soil, and were readily identified in naturally infested soils, with negligible fluorescence in soil thought to be clubroot-free. Antiserum raised to sonicated fractions of the resting spore was used in an indirect ELISA assay of soil. When bound antiserum was labelled with anti-rabbit IgG conjugated to alkaline phosphatase, there was a negative correlation between absorbance levels and resting spore numbers in artificially infested soil. In contrast a close to linear response, with a correlation coefficient of 0.971, was recorded when infested soils were assayed with bound antiserum labelled with protein-A peroxidase.