NEW MATERIAL: A compd. of formula I [where R1 is H or a 1-6C alkyl; R2 is a (substd.) alkyl, (substd.) aryl, (substd.) heterocyclic or carbamoyl; R3 is H; R4 is H or OH; R1 and R2 together may form a 3-6C straight chain alkylene, etc.; R1 and R3 together may form a (substd.) hydrocarbon, etc.; R3 and R4 together may form carbonate; R7 is H or methyl; one of R8 and R9 is H, OH, an alkoxy, etc., and the other is H; and R8 and R9 together may form oxy or (substd.) oxime], its ester or acid addition salt.

EXAMPLE: Erythromycin A9-semicarbazone.

USE: An antibacterial agent to gram-positive bacteria and gram-negative bacteria.

PROCESS: A compd. of formula II is allowed to react with a substd. hydrazine of formula III (where R1A is H and R1A and R2 together may form a 3-6C straight chain alkylene, etc.), in the presence of an acid.