The discovery of bacterial viruses able to kill bacteria, named bacteriophages (phages), more than a century ago, contributed to combating bacterial infections during the first three decades of the 20th century. Vladimir Sertić, a Croatian microbiologist, was one of the pioneers in bacteriophages investigation, who performed significant scientific research on phage strains characterization, isolation, and classification. The important contribution of Vladimir Sertić can be seen from his private archive (from the 1930s) which contains hundreds of valuable archival materials that are today kept at the Department of Pharmacology School of Medicine, Zagreb. The Discovery of this archive was recently described by Lackovic and Toljan. Here we describe a further survey of this archive. In addition to many documents, it contains phage cocktails in a small commercial paper box, with instructions for usage, as clear evidence of their therapeutic application in the pre-antibiotic era. This revelation, not shown in the literature up to now, to the best of our knowledge, motivated us to present it to the wider scientific and professional community with this short article, giving an additional brief overview of the current perspective of phage investigation and therapeutic application.