The aim of this study is to determine the difference in efficiency of direct immunoenzyme-linked assay (EIA) and conventional microscopy (CM) plus conventional concentration technique (CCT) using comparative analysis in the diagnosis of symptomatic and asymptomatic lambliosis when only one stool sample is to be tested. The study enrolled 577 examinees: 208 patients and 369 asymptomatic examinees. Lambliosis was diagnosed using CM plus CCT (three stool samples) and direct EIA (the first sample). All statistical parameters of the EIA method were 100% in the patients with symptoms of infection. In addition to that, in the group of asymptomatic carriers of Giardia lamblia (G. lamblia) some very high values of these parameters were recorded too, with sensitivity and negative predictive value being both at 100%. In contrast to the EIA method, CM plus CCT of the first stool sample demonstrated significantly lower sensitivity (66.67%) compared to the reference standard. The study did not demonstrate any statistically significant differences in diagnostic efficiancy between the EIA testing of one stool sample and CM plus CCT (p<0.05). However, the observed difference in diagnostic efficiency between the methods was very close to the cut-off value for statistical significance (p=0.06).