Our work in the programe Co-existence of the host and parasites is important for the world public and also for the Slovenia, because through our activities we are placed on the map of Europe. Because of the complexity of the program results are shown in four separate thematical parts: BACTERIOLOGICAL PART In thi s part we studied resistance of microorganisms isolated from daily clinical specimens to antibiotics. This activity is one of the most important goals in contemporary bacteriology. Data about newly emerged clones of MRSA in Slovenia are not important only for us, but also internationally. We established that in the last years increased consumption of macrolide antibiotics leads to increased resistance of Streptococcus pyogenes and Streptococcus pneumoniae strains, isolated from respiratory organs, to macrolides. On the contrary increased consumption of macrolide antibiotics does not influence the resistance of Haemophilus influenzae and Moraxella catarrhalis strains, isolated from the respiratory organs. VIROLOGICAL PART To our best knowledge we were the first who proved that the liquid hybridization technique of the second generation represent a very reliable test for the determination of highly hazardous human papiloma viruses (HPV). Unfortunately the method is not suitable for discriminating some newly emerged genotypes of HPV. We were also the first who performed research on clinical relevance of several tests used to measure the viral burden of hepatitis B virus. We confirmed that in this moment the best test for determination of viral burden represent Cobas Amplicor HBV Monitor test. We were first who give proof that presence of provirus HIV-1 DNA in the gingival fluid of patients with advanced form of gingivitis represents high risk for infection with HIV with gingival fluid. We found first that several different kinds of anti-HCV antibodies exist in the gingival fluid of patients with chronical form of hepatitis C. We established first that the reaction of telomerase represent one of the most important events in the ethiopathogenesis of throat cancer. We developed the fastest technique (35 minutes) for detection of CCR532 mutation, and reject the opinion that this mutation occurs in increased number in patients with chronic hepatitis C. IMMUNOLOGICAL PART Discovery that apoptosis of the kidney cells after activation of the complement system contribute to the development of glomerular nephritis, represent a new approach toward the explanations of the autoimmune diseases evolution. Results of analysis of influences of vaccination (against influenza, tick borne meningoencephalitis, and hepatitis B) on the immune response of patients with AIDS and on the course of their disease were for the first time published. We further demonstrated that proportion of T helper cells found in granuloma lesions caused by aerobic bacteria in mouth exceed those found in the lesions caused by the anaerobic bacteria. T helper cell from the aerobic lesions synthesizes and secretes more IL-4 then T helper cells from anaerobic lesion. We studied activation pathways in neutrophil granulocytes. We found that none of the known activators of the oxidative burst can trigger it without the increased rest activity of the cytosolic calcium. Therefore cytosolic calcium is the most important factor for the evolution of the oxidative burst. PARSITOLOGICAL PART With our research we acquired important data on what is the distribution or danger of toxoplasmosis, criptosporiosis and blastomycosis in Slovenia. Description of two imported cases of subtropical miosis from Canaries islands and Peru proved that in these days exotic diseases can occur anywhere on this planet. Data are important also for monitoring of world epidemiological situation.