Red azo spots are conspicuous against a pale green background at both the anal and excretory pores of D. immitis, whereas D. reconditum shows no such spots but stains pale-to-dark pink in the anterior 3rd of the body and a bright red in the posterior 2/3rds. Unfortunately, the solutions are unstable and must be made fresh every time. It is effective, but possibly impractical in routine practice.