This paper discusses the following ten subtitles with the contents indicated. 1. To meet a microbe: discusses the four alternatives in host-microbe interactions. 2. Receptors and signal transduction giving gene activation: discusses the lipopolysaccharide receptor and the limitations of cell cultures versus use of live animals. 3. Effector molecules--antimicrobial peptides with and without cysteines. A data base exists with over 500 sequences. This paper gives a general overview of five classes of gene-encoded effector molecules, based on the absence or presence of cysteines. These molecules are peptide antibiotics with wide spectra against different microbes. They are synthesized as propeptides and post-translational modifications are common. 4. Effectors of innate immunity--lethal action without host damage: evaluates current opinions about the mode of action of peptide antibiotics and the fact that these effectors do not create host damage. 5. Genes, introns and movable elements. Two cecropin genes containing movable elements and the human cathelicidin gene for proFALL-39/hCAP18 are discussed. 6. The natural microflora. Hippos or frogs as model systems. This section includes the isolation of bacteria from the normal flora of frogs; Aeromonas hydrophila, the bacterium found on all five frog species studied; arguments and selected examples of frog-microbe interactions in vivo and in vitro; and the use of glucocorticoids as control for nuclear factor-κB/IκBα regulation of effector genes. 7. The use of germ-free mice--hard facts from hard work: summarizes new findings which indicate that germ-free mice are born with a seat of antibacterial peptides in their small intestine. The intestine of germ-free mice monoinfected with A. hydrophila have peptide patterns that differ depending on a pretreatment with cortisone. 8. Looking...