Streptococcus pneumoniae strain M31, an unencapsulated, serotype 2 (S2(-)) mutant having a deletion of at least 5.5 kb containing the gene lytA that encodes the main pneumococcal autolysin, was transformed to the encapsulated serotype 3 (S3(+)) with DNA from the clinical pneumococcal strain 406. Hybridization analysis revealed that the S3(+) transformants also have the deletion demonstrating that lytA and the DNA region located downstream of this gene are not involved in the encapsulation of S. pneumoniae.