OBJECTIVE: To research the connection between atopy and bronchial hyperactivity (BHR) with the diagnosis of asthma in patients with symptoms which indicate asthma without obstructive ventilation disorders. To research to what extent atopy and bronchial hyperresponsiveness are risky (predictive) factors in diagnostics of asthma in the group of patients with symptoms which indicate the possibility of asthma but whose diagnosis is not confirmed. DESIGN: Prospective random study was conducted. All of the participants took a skin pricking test for inhalation allergens and unspecific methacholine bronchial challenge test. After the proceedings the participants were examined by the experienced pulmonologist who has confirmed or dismissed the diagnosis of asthma. SETTINGS: The research was conducted at the Department of lung diseases of Clinical Hospital Centre Split in Split, Croatia. PARTICIPANTS: 103 patients who were sent to the allergy clinic with presumptive diagnosis of asthma without obstructive disorders of ventilation and with negative bronchodilatation test in the period from October 2011 to June 2012 participated in the research. A total of 32 men and 71 women aged between 18 and 35 participated. MAIN OUTCOME MEASURES: The importance of atopy and bronchial hyperactivity in asthma diagnosis. Atopy was tested by skin prick test. Positive skin prick test was shown by hypersensitivity to at least one allergen. Bronchial hyperresonsiveness was measured by bronchial challenge test with values expressed in μg of inhaled bronchial challenge substance – methacholine. Through data analysis it was determined to what extent bronchial hyperresponsiveness and positive skin prick test are risk factors in asthma diagnosis. RESULTS: Asthma diagnosis was confirmed in 56 patients and dismissed in 47. There was no significant statistical difference found in asthma morbidity in regards to the sex (P=0.228) and age (P=0.995) of participants. No connection between atopy (positive prick test) and asthma (P=0.995) was found. Connection between asthma and bronchial hyperresponsiveness was proved. Probability that participant had asthma and bronchial hyperactivity was 82,1 % and it was bigger than the probability that participant had asthma without bronchial hyperresponsiveness (35,7%). The positive predictive value of broncho-provocative methacholine test is 82% and its negative predictive value was 64%. The sensitivity of the test is 60,5% and its specificity 84%. The probability that participant has asthma is 1.04 times bigger if the participant has positive skin prick test; if, however, the participant has positive bronho-provocative methacholine test the probability is 10.8 bigger when compared to the rest of the population who tested negative. In the examined population 50 participants had allergic rhinits, 22 participants had asthma and allergic rhinitis and 28 participants had only allergic rhinitis. CONCLUSIONS: There was no connection found between atopy and asthma; positive skin prick test had minimal significance in the diagnosis of asthma in examined population. There is a strong connection between bronchial hyperactivity and asthma and the bronchial hyperactivity is therefore important factor in diagnosis of asthma in the examined population. There is no difference in asthma morbidity in relation to the age and sex of the participants.