Compounds having acenaphthene and indan as their parent nuclei were synthesized for antiinflammatory testing. Compounds which showed activity were 1-phenyl-5-acenaphthenylacetic acid and its alpha-methyl derivative (carrageenan rat paw edema) and the same alpha-methylacenaphthenylacetic acid and 2-(4-chlorobenzylidene)-3-oxo-5-indanacetic acid and its alpha-methyl derivative (rat adjuvant arthritis). None of the compounds was more active than the control compounds phenylbutazone and indomethacin.