The technology of biosensors has found extensive applications in clinical diagnostics, genomics and proteomics, environmental protection, and industry, as well as in studies of biological processes in cases where classical analytical techniques are not applicable. In this communication, the use of potentiometric and amperometric biosensors for chemical analysis in agriculture and environmental science are briefly reviewed with emphasis on the determination of toxic substances, such as heavy metals, pesticides, and selected organic pollutants. Also covered are some modern electrochemical trends, particularly the use of solid carbon electrodes in DNA-hybridization and enzymatic modification (avidin-biotin technology), related to the determination of specific sequences in mRNA or DNA. An important application of solid electrodes, modified with nucleic acids or proteins, is in the field of genom investigation of agricultural pests or pathogenic organisms in the environment, or in the determination of specific proteins in organisms. The modified electrodes, in conjunction with compact, portable diagnostic instrumentation, also seem to be promising for the investigation of DNA damage, which could be important for the identification of genotoxic effects of harmful substances on organisms.