Mycoplasma suis (Eperythrozoon suis) was detected by pcr and Southern blot in 186 pigs (121 sows, 61 piglets and four boars) on four farms in southern Brazil. dna was extracted from blood samples and a 16S rrna gene fragment of M suis was amplified by pcr; Southern blot analysis was then performed on all the samples. Twenty-two of the sows (18·2 per cent) were positive by pcr, and 40 (33·1 per cent) were positive by Southern blot; only one piglet and one boar were positive. The packed cell volume and total plasma protein of the pigs and their pcr and Southern blot results were not significantly different on the four farms, but higher proportions of the pigs were positive by Southern blot than by pcr (P<0·05). The packed cell volume and total plasma protein concentrations of the M suis positive and negative sows were not significantly different.