JoHF and (JoHF + JmHF) in some substituted flurobenzenes increase algebrically as the dielectric constant of the medium increases. Benzene solvent also causes a substantial increase in these parameters. JpHH, JpHF, JmHH, and (probably) JmFF are independent of solvent. Because (JoHF – JmHF) normally lies between 2 and 3 c/s, deceptively simple spectra often occur because of the magnitudes of the other coupling constants involved. A substituent X, whose electronegativity (EX) is greater than EH, reduces (JoHF + JmHF) if it is para to F, but increases (JoHF + JmHF) if it is ortho or meta to F. There is a need for accurate studies under controlled solvent conditions if patterns in substituent effects are to be observable.