A new approach to estimation of IgA subclass levels and IgA1/IgA2 ratio using enzymatically active and inactive forms of Neisseria meningitidis IgA1 protease was developed. The approach was tested using the sera of healthy volunteers and patients with meningococcal meningitis. There was a significant increase in the IgA1 level in patients with meningitis (mean titer 1:1546 +/- A 352) compared to healthy volunteers (mean titer 1:546 +/- A 282), while the IgA2 content remained unchanged. The IgA1/IgA2 ratio was 6.3 for the healthy volunteers and 12.8 for patients with meningitis. IgA2 for the patients with meningitis and the healthy volunteers were almost unchanged, 1:86 +/- A 61 and 1:121 +/- A 46, respectively. The proposed method is economical and reliable and can be used for evaluation of IgA1 and IgA2 in clinical laboratories or for research purposes.