Two procedures to improve virus cultivation from clinical material were evaluated: an intensified adsorption with 0.2 ml inoculum and 20 h rocking in a Bellco rocker and a low-speed centrifugation of the material onto the cultured cells. Prototype strains from 5 virus families (adenoviruses, herpes simplex virus, vaccinia virus, enteroviruses, parainfluenza 2) as well as original specimens from patients (adenovirus, herpesvirus, enterovirus) were studied by endpoint titration in comparison with the standard procedure. In adenoviruses, a quantitative immunofluorescence was performed too. In endpoint titrations, the centrifugation method did almost never lead to an increased virus titer, as compared with the standard method. However, in the immunofluoresence evaluation of adenoviruses the values attained were 3- to 4-fold higher. On the other hand, the intensified adsorption method led to an increased sensitivity in most adenovirus titrations with 4- to 25-fold titer increment, with prototype and original material. The procedure was ineffective in all other viruses studied.