Prodigiosin, the bright red tripyrrole pigment from Serratia marcescens, has also been identified in Pseudomonas magnesiorubra, Vibrio psychroerythrus, and two Gram-negative rod-shaped mesophilic marine bacteria not members of the genus Serratia. Prodigiosin is sometimes bound to proteins; thus, extracts may require acid treatment before isolation of the pigment. Higher homologs of prodigiosin have been detected by mass spectroscopy. A mutant strain of S. marcescens produced nor-prodigiosin, in which the methoxy group of prodigiosin is replaced by a hydroxy group. Another mutant strain produced a blue tetrapyrrole pigment whose structure is a dimer of prodigiosin's rings A and B. Three novel biosynthetic analogs of prodigiosin have been obtained using a colorless mutant which does make rings A and B but not ring C and which can couple rings A and B with some added monopyrroles similar to ring C. The structures of three prodiginine (prodigiosin-like) pigments from streptomyces have been elucidated. All have the methoxytripyrrole aromatic nucleus of prodigiosin and all have an 11 carbon aliphatic side chain attached at carbon 2 of ring C. In two of the pigments the side chain is also linked to another carbon of ring C. The earlier literature about prodiginine pigments from actinomycetes has been interpreted and evaluated in light of the most recent findings. The structure elucidation of six prodiginine pigments from Actinomadurae (Nocardiae) has been completed. Only one, undecylprodiginine, is the same as from a streptomycete. For three of the six pigments, nine carbon side chains are observed and in four of them the side chain is attached to carbon 5 of ring A as well as carbon 2 of ring C so that a large ring is formed which includes the three pyrrole moieties. A section on identification summarized useful methods and presents information with which any known prodiginine pigment can be identified. The final step in the biosynthesis of prodigiosin was known to be the coupling of methoxybipyrrolecarboxaldehyde (rings A and B) with methylpentylpyrrole (ring C). Recent work using 13C-labeled precursors and Fourier transform 13C nuclear magnetic resonance has shown the pattern of incorporation for acetate, proline, glycine, serine alanine, and methionine into prodigiosin. Each pyrrole ring is constructed in a different way. Two of the streptomyces pigments have also been investigated; the pattern of incorporation is similar to that for prodigiosin. The biological activities of some prodiginine pigments are summarized. All show activity against several Gram-positive bacteria; some have anti-malarial activity. Prodigiosin has been tested clinically against coccidioidomycosis.