Hybrid seeds often grow faster or produce more uniform fruit, or they may be resistant to pests and disease. However, many gardeners prefer to grow heirloom or open-pollinated varieties instead, since many heirloom vegetables taste better and are more nutritious. Figuring out whether the seeds in a packet are hybrid or not only takes a little bit of detective work.
Look for the words "heirloom," "heritage" or "open pollinated" ("OP") on the label. Open pollinated means that fruit from that plant produces seeds that will grow true, or that will produce fruit that is identical to the parent plant. The terms heirloom or heritage are generally used to denote a variety that has been saved and passed throughout several generations. Open pollinated, heirloom and heritage seeds are all non-hybrid.
Look for the words "hybrid" or "F1" on the seeds packet. F1 means that the seed in question is the first filial generation between two distinct varieties. Hybrid seed names may also have a multiplication sign ("X") in them to denote that they are a cross between two other varieties. Many states in the US require that hybrid seeds are labeled as such.
Check the borders of the pages in a seed catalog. To save space, a catalog may only print the word "hybrid" in the header or footer of the page to designate that all seeds on that page are hybrid.
Seek out seed companies that specialize in open pollinated or heirloom seeds. Many companies will state up front that they do not sell any hybrid seeds. When in doubt, call them and ask.
As a last resort, you could grow the seeds, save the seeds from the fruit it produces, and then try to grow those seeds. The second generation of hybrid seeds are often sterile, or they won't come "true" to the parent and will produce unrecognizable or mutated fruit.