SummaryThe speed of the bactericidal activity of penicillin G and ampicillin has been investigated onNeisseria meningitidis. Both these antibiotics are active at the same speed.The activity curves of penicillin G and ampicillin may be split up into segments. Following a short bacteriostatic phase the bactericidal activity is noted. The increase of the antibiotic concentration induces mainly shortening of the oarly bacteriostatic phase.As an important parameter for the choice of antibiotics to be applied in the therapy of mcningites, the performed study shows that both drugs are equivalent in this regard.