Global scale decreases in total ozone have resulted in an increase in UVB radiation at ground level. To assess the risks to human health and ecosystems from an enhanced UVB radiation, an accurate and reliable UV monitoring system is required that weights the spectral irradiance according to the biological responses under consideration. Biological dosimetry meets these requirements by directly weighting the incident UV components of sunlight in relation tc the biological effectiveness of the different wavelengths and to potential interactions between them. Bacteria, viruses and biomolecules have been developed as biological dosimeters. Their responses to environmental UV radiation, indicated as inactivation, mutagenesis or photochemical injury, reflects the UV sensitivity of DNA. After intercalibration with spectroradiometric data, biological dosimeters appear suitable as personal and field dosimeters.