Asthma is a chronic disorder of the airways. Oxidative stress is an important part of asthma pathogenesis. It plays a crucial role in exacerbating the disease, as well as an important consequence of airways inflammation. Aim: The present study was undertaken to investigate the lipid peroxidation and catalase activity in serum and antioxidant level in plasma of asthmatic patients and their association with lifestyle and severity of the disease. Methods: A total of 210 subjects, 120 asthmatics and 90 healthy controls matched in respect to age, sex, lifestyle and socioeconomic status, were chosen randomly for the present study. The samples were analyzed for MDA concentration and catalase activity in serum and ferric reducing ability of plasma (FRAP). Statistical analysis was done using unpaired Student’s t-test, ANOVA with Duncan post hoc test and Pearson coefficient of correlation. Results: The serum MDA was found to be significantly higher in the asthmatics as compared to healthy individuals (p<0.01) while catalase activity in serum and antioxidant level of the plasma were markedly lower in the asthmatics as compared to healthy individuals (p<0.01). A significant difference was observed in serum MDA, catalase activity and plasma antioxidant level among the patients in relation to the severity of disease. There was a marked increase in the serum MDA in the patients with longer duration of the disease (p<0.05). Conclusion: The oxidant-antioxidant imbalance occurs in asthma leading to oxidative stress and is an important part of the asthma pathogenesis. Uvod: Astma je hronično oboljenje disajnih puteva. Oksi- dativni stres čini važan deo u patogenezi astme. Ima pre­sudnu ulogu u pogoršanju bolesti i predstavlja važnu posle- dicu upale disajnih puteva. Ova studija je preduzeta kako bi se istražili lipidna peroksi- dacija i aktivnost katalaze u serumu i nivo antioksidanasa u plazmi kod bolesnika sa astmom i njihova povezanost sa životnim stilom i težinom bolesti. Metode: Ukupno 210 ispitanika, 12|0 astmatičara i 90 zdravih kontrolnih ispitanika odgovarajuće starosti, pola, ži­votnog stila i socioekonomskog statusa, nasumično je iza­brano za ovu studiju. Analizom uzoraka određene su kon­centracija MDA i aktivnost katalaze u serumu i primenjena je metoda FRAP (ferric reducing ability of plasma). Stati­stička analiza je izvršena pomoću Studentovog t testa, testa ANOVA sa Duncan post hoc testom i Pearsonove korelacije koeficijenta. Rezultati: MDA u serumu bio je značajno viši kod astma­tičara u poređenju sa zdravim ispitanicima (p<0,01), dok su aktivnost katalaze u serumu i nivo antioksidanasa u plaz­mi bili upadljivo niži kod astmatičara u poređenju sa zdra­vim ispitanicima (p<0,01). Između pacijenata je uočena značajna razlika u nivoima MDA u serumu, aktivnosti kata­laze i nivoima antioksidanasa u plazmi u odnosu na težinu oboljenja. Postojao je upadljiv porast nivoa MDA u serumu kod pacijenata povezan sa dužinom bolesti (p<0,05). Zaključak: U astmi se javlja poremećaj oksidantne-antiok- sidantne ravnoteže, što dovodi do oksidativnog stresa i čini važan deo patogeneze astme.