Little information is available concerning factors affecting internal cotton, Gossypium spp-, boll temperatures. Such information might be useful in boll development and growth studies, as well as determining the life cycles of insects inhabiting the immature green bolls. Field studies were conducted in 1987 to investigate the relationships between weather data and hourly internal cotton boll temperatures in the Imperial Valley, CA. Copper-constantan thermocouples were inserted into individual immature cotton bolls and temperatures were recorded with a datalogger programmed to measure and record temperatures every ten minutes and to output the mean hourly temperatures. The resulting database consisted of temperature measurements from an average of 30.5 immature cotton bolls per day for 65 days from 1 July to 13 September. Weather data were obtained from an automatic weather station 0.9 km from the field and the dewpoints were obtained from the airport weather service 16 km southwest of the field. The best fit regression equation was Y = -2.305 + 0.638 X1 + 0.470 X2 - 0.598 X3 + 2.294 X4. The coefficient of determination (R2) was 0.980. The independent variables in the equation were ambient air temperatures at the top of cotton plant canopy (X(1), C) and 30 CM below the top of the canopy (X(3), C), vapor pressure deficit (X(3), kPa) and solar radiation (X(4), kW M^-2).