OBJECTIVE Group A beta-hemolytic streptococci (GAS) are known to be capable of evoking sterile arthritis. Reactive arthritis (ReA) has been reported sporadically following primary infection with group C and group G beta-hemolytic streptococci (GCS, GGS). We prospectively studied 4 cases of ReA secondary to throat infection with GCS and GGS. METHODS Four patients with arthritis secondary to throat infection were seen. Three patients were Dutch, one was Indonesian; female/male ratio was 1/3; mean age was 30 years (range 18-46). Diagnostic evaluation included culture of throat swab and serological screening. RESULTS All patients presented with a nonmigratory asymmetrical arthritis: monoarthritis in one patient, oligoarthritis in 3. Culture of throat swab was positive in all. Antistreptolysin-O (ASO) titer rose significantly in 2 patients, and anti-DNase-B rose in 2 patients. ASO was maximal (mean 1000 U/ml; range 890-1110) and anti-DNase-B was 395 U/ml (range 290-500). Treatment consisted of feneticillin for 5 days; nonsteroidal antiinflammatory drugs were prescribed on demand. All patients recovered fully in 3 to 12 weeks. CONCLUSIONS These cases provide evidence of a benign non-group A streptococcal ReA, i.e., secondary to GCS or GGS. The presence of the organism in the throat along with the elevation of antibody to streptococcal products is important for the diagnosis of GCS/GGS associated ReA. A positive throat culture is needed for differentiation from GAS associated poststreptococcal ReA, because prophylactic measures are effective only in GAS associated sequelae, but not in GCS/GGS associated ReA.