Parasporal proteins from Bacillus thuringiensis (Bt) are well studied in various fields of environmental biotechnology and recently in medical biology. Correspondingly, this dissertation presents the use of site-directed mutagenesis technologies to obtain mutant cry and parasporin proteins with different effects against vector-borne diseases and human cancer cell lines. The use of in silico modeling offers a possible explanation of how the altered residues are involved in changing their structure and interacting with cell membrane receptors. The proteins from this work can be used as targets for new studies that will provide more information about the mechanism of action of Bt proteins, and open the door to the employment of these biomolecules in combating diseases.