A solar system for greenhouse heating has been recently developed by the authors of this paper. Whenever possible the system operates as a "closed system", which typically results in above optimum air temperatures, very high air humidity and in low levels of CO2 concentration. Experiments were conducted over three seasons to assess the performance of melons in this system. In all three seasons the experimental solar system raised night temperatures (mean and minimum) approx. 6°C above outdoor night temperatures. The effect of CO2 enrichment (1000 vs 340 ppm) was investigated in the first (Nov. 1991-Feb. 1992) and second (Nov. 1992-Feb. 1993) experimental seasons. The first season was characterized by unusually low radiation regimes and minimal bee pollination. Carbon dioxide enrichment increased total fruit yield from 1.9 to 4.6 kg/m2. Most of the fruit was parthenocarpic and therefore too small for the export market. Furthermore most of the fruit produced had no netting. In the second year CO2 enrichment increased total yield from 2.5 to 3.4 kg/m2 and exportable yield from 0.5 to 1.8 kg/m2. The effect of planting date (28/9/93, 2/11/93 and 10/1/94) was evaluated during the third growing season. Carbon dioxide levels were kept at 1000 ppm. The first planting date produced a total yield of 2.9 kg/m2 and exportable yield of 2.0 kg/m2. Total yield of the second planting date was 3.2 kg/m2 and exportable yield was 0.3 kg/m2 (no netting). The third planting date gave a total yield of 5.5 kg/m2 and exportable yield of 4.5 kg/m 2. The results indicate that the new solar heating system supports melon production in Beer-Sheva during all winter and early spring months, and CO2 enrichment enhances marketable yields. It was postulated that high humidity during fruit development has a strong negative effect on the development of netting on the fruit surface.