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Key words: Isospora suis -life cycle -neonatal isosporosis -pathogenicityIsospora suis has been considered an important enteroparasite of piglets which causes coccidiosis in neonatal swine (Ruzicka & Andrews 1983). Yellowish-pasty diarrhoea is the most characteristic clinical sign of the disease which is more prevalent in piglets between 5 to 21 days old. It does not respond to any antibiotic treatment (Lindsay 1989) but experiments with an anticoccidial drug toltrazuril have been successfully used experimentally (Mundt 1994) as well as in some swine farms (Kondela et al. 1991, ByeungGie 1995 pressures of oocysts by the time of faecal examination. Life cycle and oocyst structure of Sarcocystis species were unknown at the time of their articles publication.In the present study an experimental infection of thin wall type oocysts was performed in piglets for the confirmation of I. suis species characterized by clinical signs, possible small intestine tissue lesions, oocyst structure and life cycle observations. MATERIALS AND METHODSThin wall oocysts were isolated from four faecal samples collected in swine farms and cultivated according to the method described by Long et al. (1976) with some modifications. Faecal samples were filtered through a metalic sieve of 50 meshes, centrifuged in 800 g for 5 min to obtain the pellet and cultivated in 2% potassium dichromate solution with oxygen aeration at room temperature of about 25 o C during at least 72 hr. This type of oocysts was inoculated in four-five-day-old pigs free of contamination: pig 1 received 6.6 x 10 4 sporulated oocysts, pig 2 received 10 3 oocysts, and pigs 3 and 4 received 4 x 10 4 oocysts.They were kept in individual metal cages and fed with cow milk. Daily observations of pigs for dehydration level, general conditions, faecal consistency and oocyst production were performed until the 21st day after inoculation. MacMaster and Sheather' s methods were used for oocyst identifi-

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