Culture-independent methods, employed to study the diversity and complexity of microbial communities that are based on amplification of rRNA genes with universal primers, include gradient gel electrophoresis (denaturing or temperature), single-strand-conformation polymorphism, restriction fragment length polymorphism, qPCR and high-throughput DNA sequencing. Substituting one or more base(s) within or at the 3'-termi of the universal primers by inosine can overcome some of their shortcomings improving amplification capacity. Universal primer sets do not usually amplify sequences with nucleotide mismatch to the templates, particularly in the last three bases, whereas inosine-modified primers anneal and amplify a variety of rRNA gene sequences. Inosine-containing primers are therefore might be useful to detect more species in diverse prokaryotic populations. The article summarizes the pros and cons of using inosine especially at the 3' termini of universal primers in nucleic acid amplification for the study of microbial diversity.