Primary human osteoblasts were cultured on self-assembled monolayers (SAMs) of alkylthiols on gold with carboxylic acid and methyl termini, and the kinetics of cell attachment and proliferation were measured. Over 90 min approximately twice as many cells attached to carboxylic-acid-terminated monolayers as attached to methylterminated monolayers. After 24 h the number of cells attached to carboxylic-acid-terminated monolayers was ten times that attached to the methyl-terminated monolayers. Cell morphology and cytoskeletal actin organization also were found to be different. Osteoblasts were cultured on SAMs that were patterned by photolithographic techniques. Cells attached almost exclusively to carboxylic-acidfunctionalized areas of the patterned surfaces, leaving meth-yl-functionalized regions bare. The patterns strongly influenced the morphology of the attached cells. After 24 h, cells were observed to bridge between carboxylic-acidterminated regions separated by 75 m, methyl-terminated regions but not those separated by 150 m methylterminated regions. After 6 days in culture osteoblasts formed multilayers on the carboxylic-acid-terminated regions of the pattern.