Approximately 20% of all children will suffer from wheezing illnesses, and in 1-3% of all infants, respiratory distress is severe enough to require hospitalization. As wheezing infants form a heterogeneous group with different phenotypes and outcomes, it is still a challenge to identify those who will go on wheezing to develop asthma. In order to facilitate the prediction of later asthma, algorithms have been developed for clinical use. The algorithms validated this far are based on personal atopic findings and the parental history of asthma, and blood eosinophilia has been the only laboratory marker included. In this review, we will focus on the role of respiratory viruses, eosinophil activation markers, specific immunoglobulin E antibodies, and skin prick tests, as early life predictors of persistent wheezing and asthma. According to recently published results, rhinoviral infection seems to carry a high risk for persistence of wheezing. Sensitization to inhalant allergens in infancy strongly increases the risk for later respiratory allergy. Eosinophil activation markers seem not to offer significant additional value over blood eosinophils. Determination of viral etiology of wheeze, and/or screening for early sensitization to inhalant allergens in individuals with no clinically evident atopy might be of use in identifying future asthmatics.