SUMMARY. Objectives: To study the haematological and immunological changes in the blood of cotton mill workers during the course of their shift. Method: Blood samples were taken from 70 cotton mill workers before their shift and after 4 hours of cotton dust exposure on the first day of the working week. The following parameters were measured: red blood cells (RBC), haemoglobin (Hb), haematocrit (Ht), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), red cell distribution width (RDW), platelets (PLT), plateletcrit (PCT), mean platelet volume (MPV), platelet distribution width (PDW), white blood cells (WBC), absolute number and percentage of polymorphonuclear leucocytes, eosinophils and mononuclear leucocytes, IgG, IgA, IgE, IgM, CRP, a2 macroglobulin, haptoglobin, acute-a1glycoprotein, prealbumin, fibronectin, fibrinogen, prothrombin, plasminogen, antithrombin III, a1antitrypsin, C1q, C3c, C4, C5, B-factor, and circulating immune complexes (CIC). Screening was made for the specific IgE against cotton. The level of cotton dust in the workplace was measured by the method of vertical elutriator. Statistical analysis was performed using the paired t-test. Results: Following cotton dust exposure of four hours duration a statistically significant increase was observed in the absolute number and the percentage of polymorphonuclear leucocytes, and in MCHC, PLT, PCT, IgG, IgA, a2 macroglobulin, haptoglopin, fibronectin, fibrinogen, C3c, and C4. There was a statistically significant decrease in the absolute number and the percentage of lymphocytes, eosinophils and monocytes, and in RBC, Hb, Ht, MCV, RDW, C1q and B-factor. No statistically significant changes were observed in IgE, IgM, CRP, acute-a1glycoprotein, prealbumin, prothrombin, plasminogen CIC, antithrombin III, and C5. None of the workers tested positive for the specific IgE against cotton. The level of cotton dust was on average 0.8 mg/m3. Conclusion: After cotton dust exposure an immunological cascade takes place, probably with an acute phase reaction, activation of the classical and alternative complement pathways and possibly with a low degree of haemolysis. It is hypothesized that the main mechanism of the haematological and immunological changes observed in the population under study is a type II hypersensitivity response. Pneumon 2009, 22(4):323-330.