Experimental studies have shown numerous health disorders associated with occupational exposure to organophosphate pesticides but evidence of impaired immune functions by pesticides in humans is scarce. This study determined complete blood count (CBC), serum immunoglobulin classes (IgE, IgA, IgM, IgG),acetylcholinesterase (AChE) activity and skin sensitivity prick test to common environmental allergens in 60 farm workers (30 pesticide applicators and 30 farmers) exposed to organophosphate (OP) pesticides compared with30 apparently healthy, non-exposed workers. Serum AChE activity, mean PCV level, total white blood cell count (TWBC) and neutrophil count were significantly reduced while the mean lymphocyte count and eosinophil count were significantly raised in both pesticides applicators (PA) and farmers compared with controls. However, mean monocyte count was significantly raised in PA compared with controls. Also, serum activityof AChE and mean serum IgM level were significantly reduced while the mean monocyte count was significantly raised in PA compared with farmers. This study shows that pesticides applicators are more exposed to effects of organophosphate than farmers.