Samples of five different solutions for disinfection of soft contact lenses were experimentally inoculated with a strain of Pseudomonas aeruginosa or Serratia marcescens. No bacteria could be detected after one hour in solutions with biguanids, while they survived in reduced number up to 72 h in solutions with polyquaternium as active substance. However, prolonged survival after one week could not be detected. Lenses treated with polyquaternium based contact lens disinfectant solutions overnight may still harbour bacteria, which might increase the risk for bacterial complications, such as keratitis.