Toxin from Clostridium botulinum type F was recovered from dialysis cultures and partially purifed by: (i) ammonium sulfate and ethanol precipitation; (ii) O-(diethylaminoethyl)-cellulose chromatography; or (iii) diethylaminoethyl-cellulose chromatography followed by O-(carboxymethyl)-cellulose chromatography. Toxin purities as reflected by specific activity were 1.83 X 10(6), 9.8 X 10(6), and 2.0 X 10(7) mouse 50% lethal doses (LD50)/mg of N, respectively, for toxins purified by the three methods. The toxins were converted to toxoids by incubation at 35 C in the presence of 0.3 to 0.45% formalin for 21 to 35 days. Toxoids were immunogenic in guinea pigs, as demonstrated by serum antitoxin response and the immunized animals' resistance to challenge by type F botulinal toxin. The immune response to type F toxoids was lower when toxoids of serotypes A, B, C, D, and E were combined with the type F toxoid than when the type F toxoid only was administered. The toxoid prepared from the most highly purified toxin (method [iii]) conferred the highest immunity in guinea pigs at a given dose level. A relation between serum antitoxin level and resistance to challenge was observed. At least 50% of the groups of guinea pigs with 0.015 antitoxin units or more per ml survived challenge by 10(5) mouse LD50 of type F botulinal toxin. A dose of 3.75 mug of N of the most highly purified type F toxoid in combination with the other five serotypes of botulinal toxoid invoked an immune response in guinea pigs comparable to that considered adequate for the other toxoids.