The commercial solution of fourth generation (G4) of poly-amidoamine (PAMAM) dendrimers contains methanol, which is toxic for human body. Our differential scanning calorimetry (DSC) study of dendrimers confirmed the existence of this threat. The recommendation is done on how to prepare dendrimer solutions for practical and safely use in gene delivery. DSC have been also used to study the thermodynamic properties of DNA/dendrimer complexes (dendriplexes). We showed that up to DNA/dendrimer ratio 43 ± 3 (w/w) the solution was homogeneous, but stable aggregates were formed at higher PAMAM content. DSC experiments performed with homogeneous solution of dendriplexes revealed existence of the pH-dependent melting curves that contain several endothermic peaks associated with melting of GC-rich regions.