Humidity sensors using various principles of operation are evaluated for the potential use at sea on buoys and ships. Thin film capacitive polymer sensors include the Vaisala Humicap HMP-14U (with WHOI electronics), Hy-Cal Engineerig Ultra-H (also with WHOI electronics), the new Vaisala HMP-35A, and the Rotronic MP-lOOF. Impedance sensors include the Thunder Scientific PC-2101, Phys-Chem PCRC-ll, and the General Eastern 850. The Hygrometrix 8503A is the only organically based cellulose crystallite sensor evaluated. Chilled mirror dew sensors include the EG&G 200M Dewtrak, which was used as a comparative standard, the General Eastern Dew-lO and the WHOI D10IQ Intelligent Dew Point Sensor. The IR-200 infrared optical hygrometer from Ophir is also included in this study. The performance of the EG&G 200M Dewtrak was quite disappointing. Errors of up to 2.5C in air temperature were observed due to inadequate shielding from solar radiation.