Competent Haemophilus influenzae bacteria were exposed to purified phage HP1 DNA and then plated for transfectants (PFU). When 32% (final concentration) glycerol was added before plating, between 10- and 100-fold more transfectants were observed. Glycerol had no significant effect on transfection with DNA from single or tandem double lysogens. It also had little effect on transformation with chromosomal DNA or on transformation of defective HP1 lysogens with phage HP1 DNA. It was concluded that glycerol induced the release of adsorbed linear double-stranded DNA into the interior of the cells.