This study was undertaken to define the cloning efficiency of squamous head and neck (H/N) cancer in soft agar. Twenty squamous cell carcinomas of H/N origin were mechanically dissociated and cultured in the human tumor clonogenic assay ( HTSCA ). No growth was observed. Nine ascites specimens from separate patients with ovarian cancer were cultured during the same time period, and six grew, all with more than 30 colonies per plate. Thirty-one additional H/N specimens were enzymatically dissociated and cultured in the HTSCA . Again, no growth was observed. Sixteen of these enzymatically dissociated specimens were simultaneously cultured in identical media without agar. Five specimens grew. We conclude that squamous carcinoma of H/N requires anchorage and fibroblast support for successful growth in culture. Suspension in semisolid media is less effective than liquid tissue culture systems for in vitro growth of this tumor type.