The emergence of new pathogens and the increasing antimicrobial resistance patterns of old pathogens are contributing factors to the high epidemiologic impact of lower respiratory tract infections. Hantaviruses, Chlamydia pneumoniae, and penicillin-resistant Streptococcus pneumoniae have recently gained most of the attention of international researchers. Hantavirus pulmonary syndrome has been confirmed in 100 cases with a very high mortality (52%). Risk factors for infection are peridomestic cleaning, agricultural activities, and an increased number of small rodents like deer mouse, mainly Peromyscus maniculatus. Pulmonary capillary leak and multiorgan involvement characterise Hantavirus pulmonary syndrome. Most recent reports rank C. pneumoniae among the three most common etiologic agents in community-acquired pneumonia, but it is also involved in chronic diseases such as chronic obstructive pulmonary disease and asthma. Several recent reports indicate the striking increase of penicillin-resistant S. pneumoniae strains. These data emphasize the crucial need for new therapeutic agents and more effective prevention programs.