Microfilariae can be transmitted by blood transfusion and they may be circulated in the recipient's blood but they do not develop into adult worms. Mortality associated with transfusion associated filarial infection is not documented but it may give rise to morbidity in transfusion recipients in terms of allergic reaction. The present study was carried out to investigate the association of post transfusion reactions and filarial infections in an endemic area. About 11,752 transfusion recipients were followed up and in 15 months period, 47 (0.4%) post transfusion reactions (PTR) were reported. Routine investigations for post transfusion reaction were carried out in all 47 patients and their respective blood donor. Moreover, blood culture, microfilaria detection by concentration technique, filarial antibody and antigen detection (both by ELISA) were done in all subjects. Out of 47 patients showing post transfusion reaction, 29 (61.7%) patients developed allergic reaction. Eighteen (38.3%) patients having allergic reaction did not have previous history of blood transfusion and 14 (29.8%) of them received transfusion from blood donors who was either positive for microfilaria, filarial antigen or antibody. Microfilaremia was demonstrated in 4 (8.5%) patients and 5 (10.6%) blood donors. Microfilaria was concurrently present in 2 patients and their respective donors. Filarial antibody was detected in 27 (56.5%) patients and 26 (55.3%) blood donors but microfilaria was detected in 3 (6.4%) and 4 (8.5%) subjects, respectively. Antigen detection test correlated with microfileraemic state of subjects. The result shows that transfusion associated filarial infection may be a probable cause for transfusion-associated morbidity in endemic areas. In 14 (29.8%) patients having allergic reactions, the probable cause was transfusion-associated filarial infection. Filarial antigen detection test was found to be more useful in detecting infections. Blood donors with active history of filarial infection should be deferred from donating blood. Filarial antigen detection test may be employed as screening test for blood donors, if possible.