comparing 2 tables. . .

can anyone help please??

we have two tables in our database that *should* have the exact same number
of records, with identical values in their corresponding primary keys (pk
same in both tables, int4). for this example, table t1 with primary key
pk, and table t2 with primary key pk. after about 3 months of use and a
crash last night i see that the two tables do NOT have the same number of
records -- one is missing some that it should have. is there a way i can
compare the two tables and select ONLY the records that do NOT exist in the
2nd table?? if i could identify the records (and the pk) then i could
manually insert them. each table has over 50,000 records so it is not
feasable to review each record to find them manually (which i tried last
night. . .).

we are struggling this morning -- any help you could provide quickly would
be greatly appreciated!

jt kirkpatrick / mps