In a prospective study of 107 women, bacterial vaginosis was clinically diagnosed in 34 women. Compared with clinical diagnosis of bacterial vaginosis, detection of clue cells in Papanicolaou stained vaginal smears showed a sensitivity of 88.2%, a specificity of 98.6%, a positive predictive value of 96.8% and a negative predictive value of 94.7%. The corresponding values for detection of bacterial vaginosis in Gram stained smears compared with the clinical diagnosis were 100%, 97.3%, 94.4% and 100%, respectively. Compared with clue cells in wet smears, identification of clue cells in Papanicolaou stained vaginal smears showed a Kappa index of 0.87 and compared with Gram stain criteria a Kappa index of 0.94. The correlation between Gram stain and Papanicolaou stained vaginal smears showed a Kappa index of 0.89. In contrast to the results of earlier investigators our studies indicate that the demonstration of clue cells in Papanicolaou stained vaginal smears correlate reasonably well with the conventional clinical criteria. However, the Gram stain method may be more reliable than the Papanicolaou method.