| Sarcocystosis is a zoonotic disease caused by coccidian/apicomplexan protozoa in humans and animals. The prevalence of muscular sarcocystosis among 100 patients with non-specific rheumatic diseases was determined. An indirect fluorescent antibody test (IFAT) using the Sarcocystis fusiformis antigen was used. The sero-prevalence among all examined patients was 52%. Patients with myositis have the highest percentage of positivity (39.5%). Statistical significance was between positive and negative cases in group A (non-specific rheumatic diseases) with highly significant results in the myositis subgroup. 39 out of 52 (75%) seropositive patients expressed eosinophilia (7-18%). There was no cross reaction with Toxoplasma positive serum. Muscular sarcocystosis may be an important cause of the non-specific rheumatic diseases especially myositis with increasing percentages over years in our locality. Further studies, for the source of infection, early diagnosis and treatment are necessary, as they remain unclear.