Continued intensive cropping of soils dedicated to vegetables in Puerto Rico reduces organic matter levels which results in increasing dependability on inorganic fertilizers and lowered agricultural sustainability. One alternative for organic matter maintenance in soils is to supplement these with biosolid-yard waste compost. Because we were concerned about possible deleterious salinity effects on field planted tomatoes, pot experiments were conducted for a period of six weeks two examine tomato (Lycopersicon esculenlum Mill, var. Bonanza) response to biosolid yard-waste compost addition in a Fraternidad clay (Typic Haplusterts) soil. Five compost levels (0, 50, 100, 200 and 2000 mt/ha) were added to soil in pots and tomato was grown with soil water at approximately field capacity. Plant height, stem diameter, leaf area index, and aboveground biomass all increased with each successive compost level added. SPAD chlorophyll meter readings were significantly higher with the 200 mt/ha compared to other treatments. We observed that leaves at the higher compost treatments appeared curled, with the edges cupped upwards suggestive of water stress. Since the pots were well watered we hypothesized that these were salinity induced effects, although leaf water potentials were not affected by compost levels. The results area encouraging because they demonstrate that plant vigor and biomass are increased with compost addition in the presence of adequate moisture and nutrients (N, P, and K levels) in soil. Soil pH and electrical conductivity were significantly influenced by compost addition due to the apparent inorganic character of the compost material, and the basic cation contribution. These are negative attributes that would limit long term use in neutral to alkaline soils of the semiarid southern coast of Puerto Rico.